It seems like we had no problems bumping broadcasters off of the higher UHF channels to open up space to sell to telecom companies, so how hard would it be to reallocate, say, channels 5 and 6 to public use?

I'd expect that a lot of broadcasters left VHF after the ATSC transition, because it seems like most modern TV antennas are UHF-centric designs, and channel 6 is already known for reaching into the bottom of the FM band, so it kills two birds with one stone.

The problem with anything new is that it's like the current appeal of ham radio products in general: the only community it reaches is people who already went out of their way to buy a compatible receiver. You can be relatively sure a "general" audience has standard FM and TV capabilities already.

Channel 5 and 6 LPTV stations are being given the opportunity to upgrade from secondary spectrum user (that could be forced off their frequency) to primary spectrum user (that can't be forced off their frequency). So the option to use channels 5 and 6 just closed, as those frequencies are now used in most markets.

I can't think of one major US market off hand that does not have a channel 5 or 6 station.

Phoenix has a nominal channel 5, but it's on RF 17. There's only two notable broadcasters on VHF, both above the FM band (8 and 10).

https://www.rabbitears.info/searchmap.php?request=result&stu...

I checked another source just to be sure, but you're right! Phoenix has an empty lower-VHF dial!

Prescott (Ch 6), Yuma (Ch. 2) and Tucson (Ch 4) have the lower-VHF stations in that region.