The viewers won't settle for less than Full HD and the advertisers will go elsewhere if they get the idea that they're not reaching customers.Who says they are going to do HD?
The logic of offing all of the subchannels and doing the lighthouse thing all sounds convincing as long as you ignore the fact that the public isn't being forced to move along (nor are they particularly being enticed to move along). If OTA walks away from them, viewers don't need motivation to seek their TV elsewhere or non-linearly.
The networks don't care because they're covered through pay TV and streaming but the individual stations should be shaking in their boots at the idea of parting company with their meal tickets.
ATSC 3.0 brings very little promise with it and big promises are absolutely essential to voluntary uptake. Promise of major improvements was essential to get everyone to move to DTV even though it was mandated! Next Gen doesn't offer any such wins for the average viewer until after it has finally replaced DTV.
If you still think Next Gen has it all over DTV such that voluntary uptake is assured, ask yourself what happened to ATSC 2.0 and whether ATSC 3.0 is such a huge step up from that.