What the networks want to do and what the affiliates want to do aren't always the same thing. The networks only control their O&O affiliates, not the ones owned by Sinclair, Nexstar, Gray etc.
One possible option we could see are stations downscaling a network's 4K downlink to 1080p, so we might still end up with improved PQ even if it isn't all the way to 4K. There's just no way of telling, and the people who are making those decisions haven't made any commitments one way or another. Sinclair is very focused on getting ATSC 3.0 rolled out (something they want to encourage because they hold a lot of patents so if everyone goes 3.0 they collect a lot of licensing fees) so they probably busy working out channel sharing arrangements in the market where they don't already control two transmitters (like they do in mine) They never mention 4K, except to list it as among the capabilities of ATSC 3.0.
My worry isn't whether 4K will come or not, but what will happen to HD PQ in the meantime, when they are basically cutting everything's bandwidth in half to fit on the ATSC 1.0 side of the channel sharing arrangement. For the stations Directv picks up OTA, unless they upgrade to an ATSC 3.0 tuner, they are going to pick up some REALLY terrible PQ. Maybe AT&T will make the investment to get every local delivered via fiber and obsolete OTA pickup, but we'll have to wait and see. It will also be bad for the people who rely on OTA, hopefully ATSC 3.0 tuners will get cheap before that becomes too much of an issue.