Just for the record, our copies being out of date with the upstream repository on itself is in my opinion not a direct problem we can address. Especially in case of jQuery core and jQuery UI this is a conscious and intentional decision as newer major versions break compatibility (afaik we are or should be up to date with the latest minor updates). Especially considering wide usage in gadgets, this is a though problem to solve that we don't have much experience in. Compatibility wise we're still in the very first iteration of MediaWiki's front-end (ResourceLoader, mw.config, jQuery and more happened, but we still support legacy globals, wikibits and jQuery 1.8).
The first turn over started in MediaWiki 1.17 with the introduction of ResourceLoader and the deprecation of pretty much all the legacy code from before that. However we haven't removed that yet.
Only recently have we started to more visibly deprecate stuff with an mw.log.deprecate accessor wrapper (possibly replacing with dummy values) to make it easier to recognise use of deprecated interfaces.
This is the first major move towards a more close loop with gadget authors in the community to keep up while we move thigns forward and take on responsible maintainership of different gadgets. And of course the Resource walker tour to identify outdated, broken and/or unmaintained gadgets that have been left behind since at least 2010 from before MediaWiki 1.17, which is still on-going and leaves much work to be done still.
That's not to say we should never upgrade, it's just going to take a while to get this first cycle finished. From there we can start cycling faster and catch up.