To be completely honest, the only category extensions I'd really be on board with would be Medium difficulty (which would probably be boring AF since it'll just be the annoying parts of Hard and Easy combined) and a category involving playing all the extra missions. At the end of the game, it tells you that there are like "extra missions" for each level that you play by hitting Z or whatever on it. So a category where you play the full story and then those could work, but then I don't even think those are that different to even make it worth doing.

Also to my knowledge there is no IGT timer. There is one on some of the vehicle stages, but then those times can be adjusted by getting the hourglass power up.

Long story short, I feel like we have about as many categories tracked as would be possible. There are more possibilities of course, but I highly doubt many more people are gonna run them. I appreciate some of the enthusiasm and ideas, but I just don't see it getting much deeper unfortunately.