three ideas:

1. I don't know if this exists already, but speed run for each domain challenge at every level

2. max level up for each character

3. completion of each group of achievements, like completing the entire "Chasmlighter" or "Meetings In Outrealm: Series I". Also, this could be edited to have all the achievements in a series, so all the ones in Meetings In Outrealm would be combined. (I think this would be a good idea as an alternative to possibly having a "Max Exploration" leaderboard)

I'm not a speedrunner and probably never will be, but I would love to see actual speedrunners try some of these :)