Media management is something that has not really been discussed since the conversion of Wikitech to a SUL wiki which changed the exposure of the site some from it's prior Developer account connected fishbowl status.

Wikitech historically has hosted a lot of media in the form of screenshots and similar that are not welcome on Commons. Just skimming the first couple of pages of https://wikitech.wikimedia.org/wiki/Special:ListFiles I don't see any serious abuse (meaning files uploaded by LTAs or others trying to get some kind of free hosting). Instead I see normal diagrams, logos, and screenshots that I would expect in an operational documentation site. I can see in Special:Log/upload that there is some amount of spammy uploading, but it seems to be getting patrolled and cleaned up reasonably well.

I wonder if the real change needed is setting up things for Special:Upload so that folks are better prompted to choose a license when uploading their own work? Maybe we could also have a cleanup campaign to find the uploaders of current media to establish licensing retroactively.

If we did restrict media uploads to sysops then I assume we would also need to make a lot more WMF staff sysops so that they can continue to use Wikitech to document operational procedures and maintain community facing help content within the intended scope of the project.

If group protection is added, I would suggest that wikitech follow the lead of mediawiki.org and add an uploaders group so we don't have to promote a lot of people to sysop just to upload diagrams. (T217523: Restrict local uploads to commons for MediaWiki.org, mw:Project:Requests for permissions/RfC/Restrict local uploads on mediawiki.org)

that are not welcome on Commons

Note files are allowed on Commons as long as they are used in any Wikimedia project, include Wikitech.