As an investigation for cross-wiki watchlists --
Gamepedia has a GlobalWatchlist listed here: http://help.gamepedia.com/Special:Version
The extension was written by Alexia E. Smith: https://github.com/Alexia
The GlobalWatchlist code is now public: https://github.com/HydraWiki/GlobalWatchlist. See if you can get it up and running locally and see how well it works. This will require a multi-wiki set-up (See Wikidata role in mediawiki-vagrant for an example).