The French version (at least), is effective in France (at least), on all Wikimedia wikis since several days. It appears systematically on all visited pages up to the point that the user dismisses it on EACH visited wiki.
If these notifications are global across all wikis, why dismissing it in one wiki requires us to dismiss it in EVERY visited wiki ? It's irritating when we just visit a series of localized versions of Wikipedia, just to check the targets of interwikis.
It should be displayed once in Commons, once for all Wikipedia editions, and only once for all editions of Wiktionary. i.e. at most once per Wikimedia project independantly of its language edition without needing to dismiss it everywhere when it was read.
Users with SUL accounts, and that dismiss the notification, should dismiss the same global notitication across all wikis of the same project that are operated under SUL.