Changes on wikidata that affect a page on the client wiki should be visible on user's watchlist just like local edits.
However we should be careful to:
- avoid showing changes to connected item(s) that do not affect the local page (labels in other languages, etc)
- be consistent across different interfaces (API query module, RSS feeds, RC, etc).
- provide correct links to diffs and user pages on Wikidata
- allow filtering out external changes