I ran into this reddit post recently about hitting all the sky islands before ever touching hyrule: https://www.reddit.com/r/tearsofthekingdom/comments/14khky0/started_a_new_game_and_managed_to_get_a_lot_done/

Decided to try it out myself and I think this would make a pretty interesting speed challenge. You don't have the paraglider, and are generally pretty resource constrained, so figuring out how to navigate from island to island using the few zonai devices made available to you involves a number of movement and logistics challenges.

With item duping, it might be less of a challenge but I still think it's pretty unique.

1. Beat great sky island
2. Don't leave the sky / hit the surface (map should not be scrollable to ground level)
3. Get all shrines, Treasure Maps, Sages Wills, Armor, Koroks, etc. in the sky
4. Finish by getting the master sword

Maybe simplify to just shrines + master sword to be less tedious; or sky-only master sword to be more open ended