As for online vs. over the air radio, from my personal experience, lots of what I listen to online is over the air somewhere in the country. I'm currently listening to WWAV, 102.1 The Wave, from Fort Walton Beach, FL. Why? because it's what I'm in the mood for today. What makes that station more compelling than my own local variety hits station, 97.1 Charlie FM KYCH? I've heard the Wave go from Frank Sinatra to Ed Sheeran, and Garth Brooks to The Ramones. Charlie isn't going to make either of those transitions. Plus, the station's center is more 90s-2000s pop-rock than typical variety hits, which these days is just a broader classic hits format in many markets.
Re: regulations. I read the Inside Radio article about what regulations should be eliminated, and while relaxing second-adjacent spacing requirements makes some sense, I don't see under the current situation how allowing the fill-in stations as we'll call them will allow many stations to move from AM to FM as some have proposed. Let's look at several markets I'm familiar with for examples why.
Los Angeles, there's lots of non-commercial spacing issues here that I'm not going to get into, so let's just focus on the commercial band in this market.
92.7, I could see EMF canceling two licenses here and moving the remaining license to Mount Wilson as a full class B.
93.5 same situation, currently a simulcast with one station in the suburbs and one in Riverside County.
94.3 same situation, with an additional 105.5 which we'll get to later.
95.1 is unavailable because of stations in Riverside and Ventura.
95.9 cannot move any closer due to already being shortspaced to the station in the Ventura area.
96.7 is currently an Orange County signal, I'm not familiar enough with what else is on that frequency to give any speculation on whether that would be able to move north.
97.5 is a big signal in Riverside, unlikely to be able to get anything else in there.
98.3 I think this is a simulcast of a 103.9 in the area, but I want to say there's another 98.3 in the Riverside area which would probably be able to upgrade.
99.1 I think now does have a translator for what was KRDC 1110, but last time I was in the market KGGI was audible in Anaheim.
99.9 KOLA puts a big signal over a good portion of the market.
100.7 might work, but you'd run into co-channel issues with San Diego.
101.5 same situation.
102.3 see 96.7 above.
103.1 see 92.7, 93.5, and 94.3 above.
103.9 I would think that station would want an upgrade.
104.7 there's certainly not room for another station here. Point Broadcasting does operate both stations currently on the frequency, but they aren't actually targeting Los Angeles.
105.5 this is an interesting one. Perhaps the operator of a small AM in this station's coverage area could get it, but I think it might be locked where it is due to 105.5 in the Ventura area.
106.3 see 96.7 above.
107.1 see 92.7, 93.5, 94.3, and 103.1 above.
107.9 is a class B licensed to Orange County, but not sure if the owners would want to move it into Los Angeles if that's even possible.
Moving about a thousand miles to the north to Seattle:
88.1 current rimshot, probably can't move any closer due to Canadian co-channel.
88.9 class D, not likely to change due to Canadian co-channel.
89.1 you could probably put a class A here, but would there be rules in place to give this to an already existing AM station, or could it go to CSN, which already operates two translators on the frequency? There's only one AM I could see in the market that would want that frequency, and I'm not sure if it would be any better than the current 1050.
89.9 you currently have two class A signals on the frequency. It's possible one could buy out the other, but that would still result in at least one canceled license, and possibly two. Also that still wouldn't be a competitive signal with the other Seattle signals due to having to protect a co-channel in Portland.
90.7 cannot move south due to 90.9 in Tacoma. If KSER decided to buy out KGRG for an upgraded 89.9, this license might go, but I can't see anyone getting it, as Everett's other stations are all commercial.
91.7 is already a signal from Gold Mountain that can't move due to a signal in Skadget County.
92.1 CBU-FM-1 puts a good signal over much of the northern half of the market. I suppose a class A could be put down in the Olympia area, with the second-adjacent 91.7 protection gone, but that's all I can see happening.
92.9 no, co-channel in Bellingham that covers a large portion of the market.
93.7 Seattle rimshot that can't move north due to Canadian co-channel.
94.5 the most crowded frequency in the region. There's already a translator for 770 here, but there's no way KTTH would be able to survive with that signal that can't be upgraded.
95.3 I suppose a class A could be put here, but I'm not sure how much of the market it would cover.
96.1 no, see 93.7 above.
96.9 no, see 93.7 and 96.1 above, plus you have to deal with Yakima as well.
97.7 see 93.7 and 96.1 above.
98.5 same situation, but the co-channel is closer.
99.3 see above.
100.3 not only do you have the monster Canadian, but you have a full class C from Portland to protect.
101.1 perhaps a class A, but unlike 95.3 where you have a class A on the Washington coast, you have a class C in Portland to protect.
101.9 could potentially have a class A to the north as the Canadians aren't really much to worry about in the metro, but won't be a competitive signal. Perhaps a good frequency for either KRKO or KKXA.
102.1 maybe? I'm not an engineer so can't comment on whether this or 101.9 would be a better frequency. You have co-channel problems to the southwest and east on this frequency.
102.9 would probably be best to keep it where it's at, given first-adjacent Canadians including 103.1.
103.3 could probably benefit by moving south, but you still have to protect the Portland co-channel.
104.1 no, Bellingham station covers a good portion of the market.
104.9 no, co-channel Canadian. From what I've heard, iHeart tried to get that upgraded but was unsuccessful.
105.7 no, Canadian co-channel and potential move-in under construction.
106.5 no, see 92.9 and 104.1. I suppose both 104.1 and 106.5 could potentially work in the Olympia area, but not much farther north.
107.3 could potentially work somewhere, but you run into a Canadian co-channel and first-adjacent in Portland, plus a Yakima co-channel. That would actually be incredibly tight spacing.
Portland,
88.7 no, Sandy-licensed rimshot.
89.5 no, already home to a rimshot signal. That signal could possibly upgrade, but I doubt it could move much closer to Portland.
90.3 I don't think the station on this frequency could upgrade, because I think there's a co-channel in Salem.
91.1 potentially, but again a non-commercial frequency.
91.9 I'd need to look at what's on the frequency currently. I get something at my location, but I think it might be a translator.
92.7 is already home to a translator. If co-channel spacing were relaxed to the standards used to justify many of these translators, then I could see that sticking around in its current form, but may require it to be owned by someone who owns a current AM. If co-channel rules are not relaxed, you have to worry about co-channels in The Dalles and Newport.
93.5 no co-channel in Newport to worry about here but first-adjacent in Eugene and co-channel translator in Longview that may want to exist. Certainly not going to be competitive with the big class C FMs in the market.
94.3 no, Government Camp rimshot.
95.1 you have co-channels in Winlock and Monmouth to worry about.
95.9 you have co-channels to the east and west to worry about.
96.7 this could potentially work, but you do have a co-channel in Lincoln City to worry about.
97.5 you have a co-channel in Bend and Lincoln County to worry about, but you might be able to get a decent signal there. There's already a translator rebroadcasting an AM on this frequency.
98.3 no, co-channel in Longview is audible in the northern parts of the market, getting fairly deep into the core. It's a DX signal by the time you get to Vancouver, but at only 30 or so miles, not much room for another station.
99.1 co-channel in Eugene to worry about here.
99.9 co-channel in Albany to worry about.
100.7 possibly, but you have to worry about co-channel in Seattle as well as Newport and Bend. The distance to the co-channels makes this potentially workable, but it might be tight.
101.5 no, co-channel in Corvallis.
102.3 translator is already hemmed in by co-channels to the south, east, and northwest.
102.5 potentially, not sure how Seattle co-channel factors in.
102.7 there's a now vacant allotment in Independence that could possibly be relocated. If we're protecting that as is though, I don't think that will work.
102.9 is already a translator and won't be able to upgrade due to the co-channel that rimshots Seattle.
103.7 co-channels in Eugene and Seattle.
104.5 would have worked for about 10 years, but now with the new signal in White Salmon it wouldn't work.
104.7 no, co-channel is Florence that has a big signal.
105.5 no, see 98.3 above. You also have a co-channel to the east to worry about here.
106.3 no, see 99.9 above.
107.1 no, co-channels to the south and north. Again, both 106.3 and 107.1 do already have translators on them, but I can't imagine an owner wanting to loose lots of coverage by shutting down the AM signal.
107.9 no, see 106.3 and 99.9.
I was also going to do a similar analysis for Eugene, Spokane and Bend, but it's already taken me an hour or more to write this out, so I'll leave it at that. Those three markets do have a few more open frequencies that could work, but not nearly enough for all of their respective market's AM stations.