Sorry that I'm not sure if it is OK to propose a new feature here suddenly.
On starting my editing activity, I usually check my Watchlist of all wikis where I'm recently active. But that takes time and effort as such wikis are a little many (Japanese Wikivoyage, Meta-Wiki, MediaWiki wiki, and sometimes Japanese Wiktionary etc.).
Then I think it is nice if a function to see Watchlist of all the wikis exists (like "Special:GlobalWatchlist" or "Special:CentralWatchlist"). It'll show list of recent changes for the pages of all the wikis the user is watching; also it'll be useful to be able to specify or exclude the wikis by languages or projects.