The history page can tell you if a page on your watchlist was updated since you last visited it. This now works the same way in Vector as in other skins. The change broke local designs on some wikis. This will be fixed this week. 
The new version of MediaWiki will be on test wikis and MediaWiki.org from 7 June. It will be on non-Wikipedia wikis and some Wikipedias from 8 June. It will be on all wikis from 9 June (calendar).