I like all these ideas. I don't speedrun much, though I do watch a fair number. I find Don't Starve runs borderline unwatchable because of the clouds. I'd personally like it if there was support to remove the clouds with a mod, so as to make the run more watchable.

I think character selection makes the run more interesting. I know the run is pretty short, but I think you could come up with some interesting strats based on what character you are using. For instance, I could see Wickerbottom using sleepytime stories to get to the areas guarded by the clockwork automatons. (Not that I think it would be faster, but you get the idea)

Either way, I'd definitely be interested in more categories. Maybe some sort of "item-get" runs? I can't quite think of what part of the tech tree would be the end-goal. For kill all bosses, maybe a particular world-gen could be used to make the game go quicker. Shorter seasons, more often boss spawns, different starting season, etc?