Season 8 should end with us finally meeting the mother at the train station. Just her introduction to Ted. Something simple like she says her name, then fade out.
Season 9, the mother should be a regular and we should see them in a full blown relationship. The good and bad.
It'll give us a chance to better understand why she's the one...then close Season 9 with the wedding and a closing shot of future Ted and his wife.
See, I wouldn't mind if they spent a season with the mother and showing their relationship together, but I feel it would also go against the premise of the show. I mean if you show the mother, at what point do you end the series then?
I know around season 3, when they first mentioned the Umbrella, Future Ted said that this "the story of how I became who I had to become before I could meet her." To me, that sounds like they only want to focus on Ted before he meets the mother, not what happens after.
That's the way I see it. I've never understood the idea of "Oh, no, he shouldn't meet her until the very end." Why? We can see the ups and downs that lead Barney and Robin to settling down together, and the trials of engagement and marriage and parenthood that Lily and Marshall go through together, but with Ted, all we get is a "Here she is. And she's the one. Believe it!" And we're supposed to just take that on faith? No way...
Not to sound like I'm always throwing out the Smallville argument, but in season nine they hinted at the suit, and we saw an actual suit in the final premiere, but they still postponed that until the very last episode. I think we might see something similar with HIMYM. They've already shown the spot where they'll meet, but as they've been doing so far since the premiere, they are keeping it until the end, and I think the most we'll see is a montage of their relationship in the final minutes.
Also, I remember with Smallville, they had kept him from training at the fortress because the belief was that by doing that, he would have been gone for years like in the movie, and would have become Superman in the process. They spent years postponing that until they ended up changing that altogether toward the end, despite the fact that it lead to some major unresolved issues with the character's future, like whether or not people ever saw Superman's face and realized he looked familiar. I don't know if the showrunners are willing to do the same because they might have a specific ending/meeting in mind, and introducing the mother sooner might mess up any character development arcs they still have in mind for Ted.