Bluetooth Auracast still has a chance at becoming a thing, and is a one-to-many terrestrial broadcast solution that, if implemented by manufacturers, will be available on almost any mobile device. It allows for 4 watts EIRP and it's one-way (no pairing). I could imagine success in a pedestrian-heavy environment.
Re: "...a few nationally allocated free-for-all spots on the FM and TV bands"
The bandwidth unfortunately does not exist for a nation-wide channel in the USA.
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.
I can't think of one major US market off hand that does not have a channel 5 or 6 station.
https://www.rabbitears.info/searchmap.php?request=result&stu...
Prescott (Ch 6), Yuma (Ch. 2) and Tucson (Ch 4) have the lower-VHF stations in that region.
Is there a "turnkey" solution for someone who wants a broadcast radius bigger than the "talking real estate sign" with a 100-metre radius, but smaller than the smallest commercial/non-profit products? I know there was a lot of talk about low-power FM a few years back, but I think that was still at a level of cost, complexity and licensing far above a lot of the potential audience.
If we had a few nationally allocated free-for-all spots on the FM and TV bands, I'd expect to see such products appear very quickly. Since they'd be made by legitimate manufacturers with the desire to stay in business, they'd generally be well-behaved and have controls limited to stay within bounds, but that would probably be enough to satisfy the niche of "I want to control what's on the radio." Yeah, the channels would be a complete noise mess, but we already did that with CB and the various bands we allocated for Wi-Fi.