It seems like it's possible to export a full 4K 60 fps video as HEVC mp4 on an iPad Pro according to the spec on the main page. Before buying this I would like to hear from someone who's done this, if the result is good and how much time it takes on a new iPad Pro.
I tried to export a HEVC on my MacBook Pro 2013 in FCPX and despite 16 GB RAM, 1 minute took about 2 hours. Just as a comparison.
Yes, it works surprisingly well. I export 4K GH5 footage at 60fps (59.94) and it takes a bit longer than real time. So if you have a minute of footage it takes a little over a minute. It will vary depending on how many effects, titles, and elements you have in your timeline of course.
The quality is good, the codec can go up to 97Mbps in HEVC.
Your 2013 MacBook doesn’t have hardware dedicated for HEVC processing but the current Apple systems are optimized for it so they go considerably faster. That includes the iPad Pro line.