I suppose the assumption is that it ends up like DAB radios in cars - cheap enough that it just becomes the default, the support just gets thrown in because they probably just use an SDR chip similar to the PC DAB sticks, rather than any real desire to support the growth of DAB.
Most DAB+ receivers don’t do AM at all, so if the market moves in that direction it’ll eventually be a forced move if radio survives.
My pie in the sky idea would be having a national commercial multiplex like Digital One in the UK. Putting all the ABC/SBS multiplexes on a 9C SFN with the local variants on the local commercial multiplex could free up 1 channel for doing so.
Sell the licenses on the basis that broadcasting on it counts as 1 commercial license in every market, with it counting towards the 2 station limit, unless their stations cover less than 30% of the population combined. So that would be any station with 2 stations in the state capitals out, while some smaller operators, and independent ones would be free to purchase.
Sure it wouldn’t be local stations, but neither are the mostly networked stations that already fill the dial.