Well Harriet Harman has said “Of course there should be a female Doctor Who but what we need is a man as her assistant,” so I guess it will happen. 
I think Miriam Margolyes would certainly put a fresh take on the role, she has the quirky look, the strong personality and she could even wear her own clothes including pop socks as we have seen her wear on t.v recently. I don't mean that unkindly she would probably be the first to admit she has her own style.
Perhaps Wayne Sleep or Rosemary Shrager could be her assistant. 
Personally I don't worry whether Dr Who remains a male character or becames a female Dr Who but I don't understand what the problem is in the first place. It's like saying Del Boy and Rodney 'should' become Fiona Fixer and Fifi.
Sometimes things simply are what they are and why change it if you are on a winner.