I tested the 5.5 beta1 version today, and obviously on a fresh installation using Xampp php 7.2 - Windows 7 Pro laptop, and no plugins installed:

The update theme feature from zip did not work, I keep getting a message that the folder exists, and,
I can still install and activate any theme, regardless of the supposed new theme header setting requirements - ref: https://wptavern.com/php-and-wordpress-version-checks-coming-to-themes

The new sitemap works fine, however note that these are the only 3 things I tested in the 10 minutes I played with it so far... I'll have some time tomorrow to really test the whole thing.

Final note for now: They have to put back the accordions in the inserter, because as it is now, the inserter is an embarrassment, among some other things, like we still don't have universal block padding and margin settings (unheard of for a page builder - which Gutenberg clearly is), I was hoping at least the EditorsKit would take the lead on this but nothing from them either... since I'm on a weird mood, YouTube videos as a background for the Cover block would be nice too. Ok, 2 more - being able to drag and drop blocks from the block navigator to re-order them, and being able to rename the labels of the blocks in the navigator, as with long pages (vertically) seeing Group, Group, Group... is not much of help.