So i`ve been playing a lot of DB and thieves guild on oblivion and i realised that the only adversary either faction has is the guard. Fair enough, that`s probably realistic.
However it got me thinking, Since the Brotherhood and the Morag tong are enemies, how fun would it be to have them battling it out in a secret war in skyrim.
And then having a choice of faction to join during the conflict. The Morag Tong could be more politically motivated, and the Brotherhood more about money to give them a difference. i think it would be great to have your faction leader in one play-through being your greatest enemy in another.
By the end of each factions quest-line, you would possibly have ascended to the leadership of your guild and destroyed the opposition.