What is the problem you're trying to solve?Edit
I often use wikipedia and watch my watchlist on wikipedia, but sometimes I need to watch a page on meta. So I have to go to another website to watch another watchlist,it is a bit inconvenient.
What is your solution?Edit
A beta feature like Cross-wiki notification.
There is a Cross-wiki notification now,why cannot have a Cross-wiki watchlist?
Expand your ideaEdit
Would a grant from the Wikimedia Foundation help make your idea happen? You can expand this idea into a grant proposal.