Feature summary: I would like a way to select all sites in the wiki farm (everything connected in CentralAuth) in Special:GlobalWatchlistSettings.
Use case(s): It would save time for users who are active on many wikis, so that they do not need to manually add all of the wikis they want.
Notes: This might need to wait until T268261: Add a list or autocompletion for sites on Special:GlobalWatchlistSettings is done.
@Tol, I think it's easy to do for me, but can you explain me what is the reason for this? Do you really expect there will be enough people that want to have 1065 sites in the list? It is huge settings page and a lot of running time to fetch the data.
I believe the issue I encountered was that I would watchlist a page on an wiki that I infrequently used, and forget to add the wiki to the global watchlist; the page would thus get lost and I would not notice updates.