WQHS Cleveland offers 2 1080i streams and 2 480i streams using existing tech and their picture is fantastic.Some US stations are currently offering two 720p streams.
I agree that 4K will NOT be the big mover/shaker with ATSC 3.0 but added HD channels and Datastreams/Datacasting will be.
From what I've read the new ATSC 3.0 would offer up to 6- 1080p streams utilizing HEVC compression, which is fantastic.
Sports and other fast moving video will benefit with 4K video but there are few broadcasters willing to shell out to produce content in that format. The big networks will do BIG sporting events in 4K but I highly doubt we'll see a Phoenix Coyotes vs Calgary Flames game done in 4K for at least a decade, too expensive to produce with not enough revenue on the table. I could be wrong, the League/Leagues could offer a 4K package but it will come at great expense to the consumer.