Netflix, VUDU, and YouTube have 1080p streaming (although it isn't very good.)
The ATSC specifications allows bitrates up to 19 Mbps. So OTA is plenty for 1080p broadcasting. Over-the-air affiliates could do 1080p H.264 video @ 19 Mbps (almost Blu-ray quality) if they wanted within the current ATSC specs. It's a matter of equipment upgrades, not bandwidth. Once HEVC is released later this year they could fit a 4K channel within current ATSC specs @ 19 Mbps.
Cheapness on the part of the providers when it comes to upgrading equipment has been the problem here and it will be a problem with it comes to 4K adoption. Bandwidth is NOT the problem. The bandwidth capacity is here across multiple formats: over-the-air, fiber, cable, satellite. The only place there isn't enough bandwidth to deliver proper 4K video once sufficient equipment upgrades are in place is AT&T's pathetic U-verse product.
Right now ALL DOCSIS 3.0 cable connections in the U.S. have the capacity to deliver 4K HEVC video via Internet streaming. The majority of Americans can get access to connections that are 50 Mbps or faster. That's plenty to handle the 30+ Mbps bitrates that 4k HEVC video will require.