So I've never really considered myself a speedrunner, but I have spent a long time optimizing full clears of discipline hollow. Once there was no optimizing left to be done, I decided to work backwards and see how long it would take to do an all bosses run while also assembling all the tools I would need for the hollow. After workshopping that for a while, the conclusion I've reached is that you pretty much need to play on easy/unrestricted for it to not be ungodly long, but with that in mind the route is actually really cool and deserving of its own category imo. Personally my ideal ruleset for it would look something like:

• Decouple the difficulty setting for the hollow from the rest of the playthrough (i.e. you can run the main game on easy and then swap to hard for the boss gauntlet itself).
• In place of the standard/unrestricted split that exists for the current categories, have a split specifically for the max level up assist option, with everything else being fair game.
• I'm more or less ambivalent on whether or not you still need to actually beat the game and roll credits after you're done with the hollow. On the one hand, it's an extra ~5 minutes at most. On the other hand, it raises more questions that need answers, like whether you can drop back down to easy again or need to stick to the difficulty you completed the hollow at, or whether or not you need to do the true ending.

I recognize that those rules are kind of arbitrary, but I really do think they strike the best balance between having different options and making sure that all of those options are completable in a relatively reasonable timeframe. For reference, running the hollow on hard without increasing the level cap is what I've practiced the most by far, and I've got it down to a little over four hours. (Sort of. I haven't actually done the whole run in a single sitting yet.)