Earlier quoted context omitted.
Microsoft did open source a bunch of their mediawiki extensions. https://github.com/microsoft/mediawiki-extensions Last i heard though they were moving off it.
Nice!! Made my day. Not sure how they can move off of it, partly because there’s no alternative that has a fraction of the capability
There was some rumours that they were unhappy about mediawiki's response to patches they submitted (they made a bunch around accessibility). However i looked through their patches at one point when this rumour started flying around and it looked like most were merged. Those that weren't generally had code review comments with questions or pointing out mistakes which were never replied to. I sort of suspect the patch thing was some sort of internal excuse because the team involved wanted to make their own thing.
Regardless, im really happy they decided to open source their extensions and it was nice to see that they put in effort to upstream core patches.