The problem it creates, in most speedrunning communities, is it discourages competitiveness. People are more interested in getting an easy WR on an empty board than putting in the time to beat an optimized run. Personally, I don't think the gameplay differs in this game enough to warrant multiple categories BUT if lots of people want to run it, that creates an actual necessity for it.

I personally love the idea of more people running any category that makes sense. Each difficulty would be good, though not a whole lot would change route wise other than longer boss fights. It took 3 years for someone to come and challenge my run, and Boss destroyed it! The more the merrier!!!