TL;DR: Interestingly, only about the quarter of the emitter file is used, the DescFile entry hasn't ever been touched , and the entire concept of groups is a mystery, so I removed them.
Now that I've spent quite a lot of time digging through how the analyzer is invoked, specifically analyzer configurations, I wanted to make sense out of the (in my opinion) somewhat outdated checker option issue, and more generally, checker registration.
@NoQ mentioned on the mailing list  that maybe it'd be worth converting the tblgen solution to a .def file, which makes a lot of sense:
- As far as I know, tblgen is mainly used by actual LLVM backend developers, and folks on the Static Analyzer may not be that familiar with the language.
- We wouldn't need to run tblgen to see what the file actually will turn into, that is a feature I'd really appreciate.
- Somewhat related to the earlier point, but unless you spend 10-20 minutes figuring out where checkers come from, it would seem they are created out of thin air. Changing to a .def format removes an unnecessary complication.
There are some cons though:
- tblgen files look awesome. I get that this isn't a very strong point, but it's a pretty sight compared to a .def file.
- It would probably imply very invasive changes in a lot of files doing the checker registration, because there's a lot of work the emitter does, that would ideally need to be handled inside the analyzer.
I did this change, so that I had less complications to deal with, should we agree that a change to .def is a good idea.