I'm not sure how popular this would be. I'm indifferent myself and would just add it if demand is there. My idea would be...

• one open category where you choose whatever level and powerup you like to start with
• one category with the restrictions of Any% Glitchless since it's by far the most relevant category

Possible ruleset:

• Time starts when entering a level (1st frame when Mario raises his arm on the zone map)
• Time ends on the first frame of the fade-out after reaching the end of a level or defeating a boss
• It will be attempted to time runs down to the frame (hint: recording in 60fps is encouraged)
• Runs are restricted to the regular exits (exception: Macro 1 in the Any% Glitchless category)
• Invincibility stars from killing 100 enemies are not allowed (exception: Wario's castle in the Any% Glitchless category)
• Carry-over glitches are not allowed (pipe glitch, bubble glitch, bell glitch, star glitch)
• Zips may be exploited in the open category (not sure if this is even relevant)

Please let me know how you think about this and feel free to suggest amendments or changes to the restrictions. I admit that I haven't spent a lot of time to think this through. :-p

Just not a fan of IL leaderboards personally. As you've described, there are too many iterations to make it tidy (which exit, which power-ups you start with, etc).