Thanks Axl. Yes, I am required to use IOS 11, since my app uses ARKit.
I’ve managed to build the Asset Catalog by hacking at the UBT IOS scripts, but when I uploaded my asset cataloged .IPA to iTunes Connect, I got a warning saying that it’s missing a marketing icon. I then hacked at the scripts some more until I got the marketing icon added, but iTunes doesn’t seem to notice it. It still tells me it’s missing.
This IOS dev at Stack Overflow had a similar issue - ios - Missing Marketing Icon - Stack Overflow
Could be that the new warning is due to my using a beta Xcode.