Some examples of challenges could be:
daily challenges:
- Create 5 restore health potions today- +200xp
- Kill 10 cave rats today- +300xp
- Kill an ice troll without taking any damage to your health- +300xp
- Successfully pickpocket 50 gold from unsuspecting people- +200xp
weekly challenge:
- Slay 200 enemies this week- +1000xp
Just an example of one set of challenges that would change every day. It'd really help keep the game interesting in my opinion and it's what I'd most love to see in skyrim.