RE: HBO and other premium channels of the time: As mentioned in the Wiki you quoted, the idea was the subscriber would pay for no commercials. By the time Cable kicked in in the 1980s, the concept of the premium channel had changed. There were plenty of ads.
It's the same with streaming services. They can't keep operating with 50% of their revenues going to royalty costs. So even the paid subscriptions will have to include another revenue stream, i.e. commercials, which I believe most subscribed streams include to a certain extent. As streaming transforms from the dominant music and content consumption model to the ONLY one, where are subscribers going to go when they threaten to defect? Pirate sites, perhaps.
Or FM radio. Keeping the medium alive for a decade longer. And that would also keep AM alive for the immigrant communities, many of whom (I'm guessing) probably can't afford many paid subscriptions.
The local (and regional) Punjabi stations, for example, don't just cater to older demos. A LOT of the music they play is Hindi and Punjabi hip-hop pop and rap. Obviously their demo skews younger then your average AM listener. If FM remains vital (and packed, like in my metro), that leaves AM for the immigrant and other ethnic populations.
If streaming decides to jack up the rates, free is always a preferable option. Radio is still free. I think BigA mentioned that in one of these threads last year, that FM radio's free nature works in its favor against streaming.
Just speculating here, obviously. I don't claim to be an expert on this, and I have no crystal ball.