At TheTestWiki there is a CheckUser test extension, where you can test the CheckUser extension on yourself. If possible I'd like this extension to also be on our testwiki, in case people want to see how the CheckUser extension works. I remember asking about this and it getting denied but I don't remember the reason.
Just because it was last updated four years ago, doesn't mean that it is unmaintained. In fact, I would like it to be enabled globally on all wikis at least until wiki founders are allowed to have full CheckUser access locally on their wikis.
I’m going to look into possibly forking and maintaining this, as I know enough MW and PHP to probably do so, and I do think that its a useful feature to have at least on publictestwiki. Anyone who comes from WMF will have heard of CU at least once or twice, and it’s one of the most popular things that I think people would be curious about, especially because almost every wiki hosting service, with the exception of MyWikis.com doesn’t allow wiki creators to access the tool. Therefore, I don’t think this falls under the category of “not useful”.
Okay, status update: The code is definitely workable. It needs to be updated for the latest version(s) of MediaWiki, but that’s the largest issue that I could find. The only other thing that I’ll note is that the current code doesn’t give users with the checkuser-limited permission access to Special:CheckUserLog, which is one of the key elements of the CU extension. I’ll look into adding code to allow a restricted log access where one can only see log entries of checks they have run, and since they will have only run checks on themselves, no PII will be divulged.
That being said, I am unfortunately currently dealing with some personal issues right now and therefore I’m not at my best and have not been as active as I would like to be. I likely will not be back to my normal activity levels until after the holidays, and even then I’m not sure how much I’ll be doing when, and therefore I cannot give an exact timeline on this.