Here's mine:

The ability to use Gutenberg blocks on Post type Archive pages, both before and after the entries’ loop, and better handling of post type archives in general. For example, a simple thing that I deal with often is that you cannot allow the site Author to set/change the archive title unless you make some custom field and modify the template.
Better handling of relative URLs. I know that it won’t happen but nevertheless, it would be nice to not having to do a database search and replace every time we switch domains (e.g. from staging to live).
Make tags and non-hierarchical taxonomies in general respect the order that they are being added by the user (here’s the issue: https://github.com/WordPress/gutenberg/issues/21589).
Sometimes, on poorly or irresponsibly written plugins, notifications persist even after I close them. Those times I would love a “Mark as spam” functionality, but that would be too much and it could easily be misused, ending up making things even worse. A less aggressive and maybe more realistic approach would be some sort of “Mute this plugin” option: Users could disallow specific plugins from displaying notifications overall, either permanently or until their next update (in case they indeed need to announce something actually important).
A better way of setting site-wide options for blocks. For example, I made a block that uses MapBox and I wanted to have an option to declare the API key, so I made an options page on the admin. It would be nice if I could set this directly from the block’s options, and the setting to be kept across all instances of the block.