Speedrun of complicating Main Story with new account would be nice.

I haven't noticed a way to create a fresh account to speedruns like this

You can move or delete save files. This is only possible on PC.

Yes, in PC is "easy" to have a clean save.

I noticed that the speedrun page has also a space to upload saves, maybe it would be useful to have there a clean save?

(It's under Resources>Saves)