Maybe this questline would involve capturing Maven and either send her on exile or execute her. Maybe we could get a Dark Brotherhood mission to assassinate her. Maybe we could get a deeper backstory for Mjoll (who would likely aid you). Maybe we could get Stormcloak/Legion support in form of soldiers. There are a lot of possibilities...
If you have already joined the Thieves guild but regret your choice, maybe you could betray them or choose to work undercover?
Maybe the thieves guild players could get a new questline that focuses on sabotaging for those who want to destroy the Thieves Guild (so it would be a different version of the same questline)?
In the end of the questline, maybe you could get to choose what to do with the Thieves Guild HQ. Maybe you could use it as a player home, maybe you could renovate it and make it into an additional market (and the Ratway would be renovated for apartments maybe?)
What do you think?
