I think going through the 2 player campaign (with different categories for one or two person runs) would be a nice, fun, quick speedrun. Could a category be created for it on speedrun.com?

2-player games are progressively unlocked (you need to play them as a 1-player game first) which makes it a bit awkward as it's own category. It could be a part of a 100% category, but at that point you're just splitting hairs.

Edit: Just to clarify what I mean by "splitting hairs". All Perfects is already a ~4 hour run and adding the 2-player medals would add ~16 minutes to make it 100%

It wouldn't be too hard to do, as you could add it to to the misc. category as Any% with 2 player, or make a just 2 player thing.