Therefore, I think its only fair that we get to see Ted's final story and see him develop and finally be with the mother and see how he got that way. We've seen so much from all of the characters and how they developed and changed to finally get to the point where they're settled down and married/have kids. I think we'll see the same from Ted.
Following this train of thought, the girl doesn't matter. The person who has to change is Ted. The other characters have all grown into adults, Ted is still a child. Once he is a responsible adult, he can meet the mother. The girl herself is irrelevant.