I'd definitely do it.

The IL leaderboards for Category Extensions were removed because 1.) very few people would run them and most were empty or only had 1-2 people with runs (many were made with low effort to get free WRs) and 2.) there were organizational problems with the boards themselves (creating things like Core NG+) that would require complete reconstruction of the leaderboards internally. I was informed over discord about this since I had submitted to a majority of the IL categories, and I assume others were as well, and they wanted to know if we had any major qualms with it being deleted.

Update from 45 minutes later: I now have video proof

tfw you finally get a legit 0:29 but gotta have video proof ;(

https://imgur.com/a/vmVmyzk

Just means I'll have to do it again ig, at least I know it's possible now.

I definitely like the idea of longer categories, especially ones involving Full Clears, B sides and C sides

Oh yeah just as a follow-up, these would probably be best suited for normal play rather than assist-mode, even though that seems to be what these category extensions seem to be centered around.

Just kinda throwing ideas at the wall here, but I was wondering whether there could be like an "A-Side 100%" where you full clear every A-side chapter. I was also thinking of level-specific 100% (something like full clear A side, then B side and C side on a separate file using the cheat code to unlock all levels, but the time is just for a singular chapter's sides), but again these are just some ideas of mine.

When timing, is it all RTA, or is it the summation of all IGT for the levels? To clarify, is it straight timing start to finish, or do we just add the levels times using the Manual Timing feature in LiveSplit?

Yeah, PC version allows you to use multiple different controllers and you can use the autosplitter easily. Unless you plan on playing casually a lot when on the road, I would say go with PC version.

I would personally suggest PC, but I guess it depends on how much you travel. If you plan on doing speedrunning though, I would definitely recommend PC version.