Was wondering if anyone had any potential ideas. The only one I had was for Deathswap, but the timer would have to be different, since deathswap doesn't start on load.

What about a CO-OP speedrun category to defeat the ender dragon? it could be random seed or set seed. There's a video of a random seed run like this:

Set Seed would be slower than single player so it wouldn't matter. But RSG Coop is a pretty fun category.