He's saying, "you know what I'd do first" to say that if he knew who the mother was, he'd have gone and run to her place and done that speech for her because he was that lonely on that particular night. This show isn't deep enough or good enough to somehow pull off an ending where the mother is met, courted, married, and then dies (in the future, I suppose) all in one season (plus an episode or two where Ted presumably meets her to cap off this season-- I could see it being an hour long season finale this year).
I thought this episode had some potential, but the story around the future versions of Ted, Barney, coat check girl was pretty poorly executed and never really explained at all. Not that they needed to be explicit, but it was just one stupid "revelation" and new future version of each character after another, and it just didn't work at all.
In short, there have been much better episodes this season, though the ending was certainly interesting. However, we already pretty much knew everything it "revealed," save for what I'm assuming is a timeline for the finale. That would put it at about May 13th if I'm not mistaken.
Oh, I did like the Billy Joel a capella number at the end though.
[This message has been edited by Inspector Spacetime (edited 3/26/2013 12:31a).]