I was wondering if there would be leaderboards set up for ILs since it displays the time at the end of each level. Would it be relegated to just one mode or would there be ones for both Arcade and Story mode?

We have yet to decide upon that Sonik. But in the future I could see it as a possibility, still a lot to see "what's to come" with this being the first week of the game's release.

Yeah, this is something that's likely going to happen. Probably just split it into Story and Arcade, by difficulty, and use IGT. Not sure about individual characters.

Can these be Category Extension like SMB3 has?

I would love to see IL leaderboards, just wanting to throw my voice in there.

I think for the sake of simplicity, ILs should only be for Story Mode so that the leaderboard doesn't get too cluttered.

I would love to see IL's eventually. I think the addition of IL's could light a spark in the community a little bit so I figured I should revive this topic. Hopefully with DLC on the rise this game gets more popular for speedrunning.

The Leaderboards are now up.

https://www.speedrun.com/shredders_revenge/levels