run idea: specific world runs. these could be custom made by or submitted to mods every set interval (lets say a month) as a community even to see who could get the best time

I don't really understand what you mean by specific worlds. Like a pre built map?

yes. this could allow for secret seeds to some extent, even if it is thr same seed

Doesn't seem to be different than playing regular set seed, where everyone already plays on the same seed (i.e. the best currently known), and not many people are interested in it

This was already attempted internally on the discord server, people tend to stop caring after a few days.

ah, thats a shame