There's one thing that is not a windfall. A FM radio station with primary status has different rules than a translator. Granted the AM side is doing what is required so we're just moving that expense to FM and requiring some equipment outlay. There's more cost and legal requirements for a primary status.
For this to happen, fairly, I suppose, all translators and LPFMs would upgrade to primary service. That would mean any of these huge translator networks with stations all over the country could either upgrade to meet primary status and rules, sell or turn in their license. Any LPFM would (to be fair) be able to jump to 250 watts and/or increase tower height, if possible, and meet primary status requirements. This actually would not change the FM radio dial as the existing stations simply change status from secondary to primary. Very few LPFMs outside more rural locations could increase power/tower height. After all, the three translator windows for AM stations are done. What the FM dial is now is what it would be with primary status. I make this statement having seen auction lists of station locations for a new FM radio service the FCC has released in recent auctions. Most are so far in the sticks, they are just beyond the sticks. In major cities it takes a crowbar to slide in to a spot.
The only upside would be those translator owners who might divest of some of that vast network of translators to transfer them to other entities that would originate programming. These big translator network owners are generally Christian radio non-profits. Some have so many translators it puts them right up there with the big corporate radio companies, if not larger as far as number of stations operated.
To change the classification, I believe Congress would have to okay this and then you'd have what might be years of yelling and screaming from each side. I can imagine NPR affiliates that have statewide networks complaining they don't have the funds to take translators to primary status, that they are in areas that cannot even support the translator anyway. I can see every full power FM saying no way, Jose. I can see LPFM stations saying they've been handicapped by secondary status and mention how many LPFMs had to go away because a full power FM decided to move. The FCC would find themselves in a big ol' can of worms trying to appease as many as possible in hopes their legal department can handle all the challenges from disgruntled broadcasters. There would be action groups like Prometheus and the NAB that would grab the FCC's ear. The NAB would have it rough: bite their AM members and help their FM members or vice versa.
Consider what a 250 watt translator is in many cases. Sure, a few have almost full market coverage in some rated markets but most do not. In larger cities, you might only reach 10% of the population you once did with the AM station. Your game plan has to change. You need to think coverage area. That AM with 75% coverage of a big city like Houston, now only covers Katy, for example. You must be a Katy station now. If there are 3 translators, chances are the 250,000 you reach means 3 stations trying to carve out a local niche amid the long established full power FMs that cover the market and have satisfied Katy listeners all along. In many respects, you're jumping from the fire (the AM) in to the frying pan (the FM translator). The only real positive is you have lower operating expenses and can allocate that 'windfall' from selling real estate to finance your ramp up to be a local station. In that respect, it might be really good for the country. You'll have broadcasters that have to serve previously ignored communities and open yourself to lower spot rates the struggling local business needs to grab the market share to survive and flourish. It will be more economical for ethnic/minority communities served by that translator to lease a station to serve that underserved community.
The unanswered question is with AM listening being as low as it is, will a translator with partial market coverage actually equal or eclipse the potential in listeners that the AM station enjoyed? This, in my book, is where the upside is not so evident. Since listener numbers equate to billing potential, is there any more opportunity there than the operator had with AM alone?