If we could add more challenges that are insanely hard for more end game things the number of items can get changed but these are some ideas

25k island level or higher

2 stacks of blue ice

1 stack of obsidian

6 beacon setup

A stack of each ore type

A stack of each type of quartz blocks

16 of each color concrete

16 of each coral type, not blocks

16 of each villager work block

A stack of each Blackstone block

The rewards can range from stuff but some can be ancient debries, god apple (so you can get the advancement of all the food), some mob eggs, more shulkers, player head, pigstep, nether items and other filler stuff like diamonds

Thanks for the suggestions here Yacob1! We are working on new challenges to update soon. Team Skyblock is on it!