Well I am happily surprised. My TV in fact DOES play 4K video files from a USB stick.
Not wanting to get the thread off course, but this did come up earlier in the thread. My TV is a Vizio M70-C3 Costco special. Previously I had only tried to play 4K videos copied from my iPhone which takes 4K video in MOV format, didn't work. And from my Phantom 4 which we all know takes video in H264 MP4 format, didn't play those either.
This thread got me wondering if my TV would play 4K MP4 files encoded using H265. I grabbed a test video off my iPhone and using Format Factory (which is an awesome free audio/video video tool) I re-encoded it and sure enough, it plays 4K MP4's off my USB stick, hooray!
Edit: My TV DOES play H264 files in 1080, but apparently it's got to be H265 for 4K, weird.