I just looked at a poll that showed more than sixty percent of the people answering think Barney and Robin will get together. Only a little more than twenty think Barney and Quinn will get together, and the rest voted for an unknown third option.
As far as timing goes, I like a 2015 birth working with a 2013 meeting of the mother. That gives Ted and the mother a year to date, and a year of marriage before their daughter is born. Obviously it doesn't have to happen like that, but I like that timetable, mostly because it works nicely with the year-to-year, season-to-season format of television.
Weird thought: I've heard something about footage being filmed early on showing the children's reaction to learning who the mother is. That way they wouldn't have to get the actress and actor who play the daughter and son later and wouldn't have to explain why they may have aged several years over the course of the story. What if Lyndsy Fonseca, the actress who plays the daughter, plays the mother as well? I'm not even kind of saying this is my prediction, but it was, as mentioned, a weird thought I had. It would be easier to age progress her rather than age regress her. She'd definitely share a family resemblence. They would have been able to film the end in its entirety years ago. They'd be able to make Back to the Future references. Again, just a weird thought, and it doesn't work with the fact that an early plan was to have us learn Victoria was the mother if the show had been cancelled at that point.