jquery.tipsy is pretty old, pretty awkward and pretty ugly. We should stop using it in our interfaces. OOUI's popups implement most of the features we'd want.
For simple contents a title attribute without payload of an extra JS dependency is sufficient as well.
(Old/minimal documentation page at https://www.mediawiki.org/wiki/Tipsy )
I'm only aware of two places still using it:
Two features that we're missing in OOjs UI that might be needed to replace tipsy:
Gadgets (and possibly even user scripts) should be taken into consideration as well before tipsy is completely removed. Will require Notice.
As the on Commons:MediaWiki in time most active competent script user @Rillke is now inactive and he used $.tipsy widely on some gadgets, it needs a real documentation for replacement!? It is a bit annoying that gadgets get not working, for example https://commons.wikimedia.org/wiki/MediaWiki:Gadget-GlobalUsage.js
I really hope tipsy support will stay until a good replacement comes, because it can do something beautiful that title attribute can't, tooltip in desktop browser version on mobiles and tablets. And because wikimedia registered users usually work there on desktop version, knowing that mobile version is good for anonym readers, but has not enough functionality for editors, it can be a very breaking change.