Yes, I remember the Progression update in Cube's backlog as well. Adding challenges or daily quests or anything similar to this would truly be a great addition to the server. Currently, you have your games and statistics there and you earn experience for every victory, but that is about it. I mean the games are great and all, but I'd sure love something else as well, maybe something that would get me to do a certain task or maybe play a game in a different way.
I do like the idea of getting some rewards for completing the challenges but I might not be the biggest fan of giving people a lot of cosmetics that are normally tied to bundles and ranks as rewards for the challenge completion. The fact is, that Cube still has to make money to keep the server running and some cosmetics should just remain something you can buy from a store. Yes maybe a cosmetic here or there wouldn't be anything wrong, but that should be it. Now, what I would suggest doing is tying up challenges to the levelling system. That has honestly been quite a forgotten part of Cube and it could be given new life and usefulness with an update like this. New challenges would also tie in very well with a
Cubecraft Level Revamp that was suggested some time ago by
@ItsJustWildd, so maybe something to think about if this ever gets added.
So yea, I think this is all I wanted to say for now. Again as said, I think it's a great suggestion, that still leaves a lot of room for improvement and developers to work on and I hope we see something like this on the server one day!