I think the traveler run would make a good speedrun. Originated as a challenge from The Basement on youtube. AwesomeSpeedVerse mentioned it above. I think this is better than the all towers category because you can choose which tower to start from and there's no need to wait for towers to activate or finish the great plateau as part of the run. And with new glitches (BTBs and BILs) this kind of category is actually interesting.

It's not too short and not too long. More skill (ability to use glitches etc) and better route planning all come into play to make a faster run.

I've been trying this one and my best time so far is just over 38 minutes. I'd love to see what kind of times pro speedrunners can achieve. I bet it can be done somewhere between 15 and 20 minutes. Would make for a good competitive category IMO.