The wikibase code that handles watchlist query was written when:
- options were not exposed to the hook
- were arrays instead of objects.
- SpecialRecentChangesFilters and SpecialWatchlistFilters hooks were used instead of ChangesListSpecialPageFilters (see I9cceda5d2dcf)
- SpecialRecentChangesQuery and SpecialWatchlistQuery hooks were used instead of ChangesListSpecialPageQuery (see I9cceda5d2dcf)
We should change from the old hooks that needed separate handling for Watchlist and RC to the new generic hooks.
We can also now make use of FormOptions, which would allow us to hook in more cleanly.