@Gargron well I'd love to give feedback but I can't as I can't load the UX as my instance is not on 5.0.
I am seeing a number of issues being tooted about that I would probably want to support eg. preserving the ability to make full use advanced 4-column web interface that I use but doing so without seeing it for myself is not really fair.
Hopefully some at least of these issues will be sorted out before I land on 5.0 but perhaps you need to keep the review/revise window open until other instance users get the new UX and can provide informed feedback.