Of course, if your FM's are translator based, selling the land would probably mean re-locating the AM to another site. Increasingly today, that's becoming a very expensive option.
I am of the opinion that when it gets to that point, the idea of licensing translators on their own (Class A1?) will begin to gain traction at the FCC.
This is off the top of my head, but what if these were the pre-qualifications:
1. Translator has to already be "attached" to the AM it would be replacing, for some predetermined length of time before conversion,
2. Translator has to already protect full-power signals, as is the case now, and after relicensing would not be allowed to make future changes that would put the signal contour outside of the previous attached AM. But it would receive protection of its licensed contour at the time of relicensing,
3. Maximum ERP 250 watts, same as now, directional antennas allowed, same as now. If the existing contour is at a high elevation but causes no impermissible signal overlap (causing interference) that would be grandfathered in and moving to a higher elevation would require a decrease in ERP (which would probably be necessary under the "previous AM contour limit" provision anyway).
4. Regular call letters, initially those of the AM it would be "replacing". If those calls already exist with the "-FM" suffix, substitute the suffix "-FX" or something. TOH ID under 73.1201 required aurally, no more FSK.
I'm probably way out in right field with this at the moment, but I think circumstances will take us in that direction eventually.