I'm excited, there's a new RFC being proposed that'll solidify MediaWiki's support for installing extensions and skins with Composer: T250406 RFC: Hybrid extension management.
At the same time, there's a conflicting RFC to, on the face of it, prevent that: T250406 Remove ability to install extensions and skins with composer.
Luckily, I think the second one is actually aiming to get rid of the possibility of extensions specifying MediaWiki itself as a Composer requirement, and so there is actually no conflict.
All a bit confusing, but a step forward hopefully for casual sysadmins who want to maintain a MediaWiki installation and easily keep all its extensions and skins up to date.
Maybe it'll also mean that extension authors actually tag their extensions with SemVer version numbers, which would be brill and make it easy for sysadmins to control what sort of upgrade they're doing.