I'd totally be down for this as a legit category and I've honestly wanted to do something like this myself! There's just a few kinks that would need to be worked out first.
The issue I see with this category is why I never got around to recording one. Even after planning routes and everything to do everything you needed to do as fast as possible, I found it faster to just either SD a bunch or to something like this () where you can spam vs matches over and over. If you wanted a more legit category out of this it would have to ban VS matches. Though that leads to problems with how do you handle getting Mewtwo then?
The only way I see it working out is if we were to allow players to start the timer as soon as they face Mewtwo (aka leave characters in 20hrs collective of VS matches and THEN start) that way you can avoid having to worry about semantics and the rest of the run could be done in a relatively reasonable time frame.