Got it, pretty simple. Here is what I did.
Just shoot 4K video from your 6S device. Then sent it to my Mac desktop via AirDrop, and just took that raw file to YouTube and uploaded. Takes a bit. First 720p shows up on the quality tab on YouTube, and as they do their backend stuff 1080p and such show up.
Then went to my 4K TV set's YouTube app and voila. My 4K video of my daughter is there.
Stunning quality too!
Hope it helps someone.