Still, I think that there are going to be well over a thousand.... maybe as many as half of all AMs... which will silence their station if allowed to have a full license for the translator.
Quite a few AMs that got translators have done modifications to reduce power, eliminated directional systems and make AM transmitter site relocations to make the AM run as cheaply as possible so as to retain the license to sustain the translator. If they could eliminate the AM altogether, it would be cheaper.
The problem today is that translators linked to AMs or to an HD channel are not "guaranteed" assignments. If a full licensed FM facility decides to move its transmitter or increase antenna height and adding coverage where the translator is located, suddenly the translator is S--t Outta' Luck. They have to move, if there is another frequency available, or shut down.
I think Scott can add some further details on how translators could be protected and given permanence. He does this every day as a profession, while I deal with rumor, innuendo and hearsay and only about 10% actual knowledge of the rules! (You will find a lot of managers basically can't do anything useful on their own and their most important skill they have is hiring people better qualified than themselves to do the actual work)
It's partially a matter of law, partially a matter of policy, partially a matter of physics.
There's not room on the FM dial to accommodate all of the AM stations that want to move there, at least not within 88-108 (and I have long considered the 76-88 band a non-starter - it's one area where Michi and I do not agree.)
You could declare all existing translators to be protected from interference immediately, if you were willing to forgo opportunities to upgrade existing full-power stations or add new ones. That's a policy matter, not a physics one, and there's an argument that eliminating the possibility of those upgrades runs afoul of the FCC's responsibilities under the Communications Act to fairly distribute spectrum, because it's not the most efficient use of that spectrum.
And here's where Michi knows more than I do - you also run up against the acts of Congress that require primary users of commercial radio spectrum to pay for it at auction. Translators wiggled around that rule because they're not primary users, and you can't just wave a wand now and declare them primary without an auction process.
Now: could you conceivably make the case that if you take an existing license that's operating on AM and simply declare it to now be an FM license instead (while surrendering the AM frequency), you could redefine "minor change" to cover such a move? I'm not a lawyer, just a consultant, but I'm sure it would have both some support and a lot of opposition from the LPFM community and elsewhere.
In summary: the road to any such change has to go through Congress. It's hard to imagine such a divided House, especially, making anything like this a priority in the near future.