An indication of which world quests you have yet to receive warband rep with. Perhaps through a blue border around the icons that you haven't gotten rep with

Possibly a list showing the same on the side of the world map

If you track any reputation an eye icon will show up on world quests that give rep with that faction.

That eye is showing on all quests for that faction though, even ones that have been completed on other characters, and therefor no longer reward reputation.

And I still need to cap out rep with 2 of the new factions, so the system that allows me to track a single isn't that helpful :D