There are three brand names that matter in film right now: Disney, Pixar, and Marvel. Disney has seen Pixar's quality start to decline a bit and I think they should be wary of the same thing happening to their other asset, Marvel. (Although Marvel was already more in tune with Disney's approach; far more than Pixar was.) Marvel's expanding to three movies a year and I could see adding more than that stretching the people in charge a bit thin.
That being said, if Feige and Co. think they can handle it, Disney should give them an offshoot brand for a movie or two a year (for starters.) Don't mess with the Marvel brand name but give the people in charge a chance to expand their scope outside of Marvel characters. If it works, you could establish another trusted brand name. If it doesn't, you don't hurt the Marvel brand.