There was an AM band improvement proposal, and one of the suggestions was to synchronize AM broadcast station carrier frequencies using GPS, to avoid beat interference.
With a small network you could use GPS, or find a way to send a reference frequency, along with audio, out to each transmitter, and sync each transmitter's oscillator to it.
There are supposed to be Part-Fifteen transmitters with carrier sync for a local cluster network, does anyone know how they do it?
The Rangemaster has a mod or module that allows the sync carrier to be sent wirelessly.
I haven't looked in to how the Rangemaster sync system works yet, but it's cool they have it, I know someone was talking about it on a video or another site I saw. That's for some pretty serious broadcasting, and maybe when your own town solicitors are involved and can provide space to put other transmitters.
Maybe that's a direction that AM broadcast as a whole can go in, a town could have clusters of low power transmitters in them, maybe more than 0.1 watts, but still a box for a pole or rooftop, and have them synched.
It's what wifi mesh networks are doing, cell phones and even FM more now with translators. With AM transmitter nodes, a station could change the shape of their coverage pattern by adding transmitters where needed, and it could be treated as one station.
Feed for thought