Another season is the worst possible news. Frankly, Ted Mosby is my least favorite character in the entire show, and lately his moping around has made me honestly hate him. I sat through seven seasons of his jackassery for the awesome supporting cast. Back in season one, I was rooting for him because he was pursuing another character that I liked. Now when the mother is clearly going to be some random introduced in the last few minutes of the series finale, I can't bring myself to give a shit. And even if they devote an entire season to letting us get to know the mother, it's still a good 2-3 seasons too late.
Unless there's some hugely consequential stuff going on with the supporting cast in the final season, I'll probably just wait until the actress who plays the mother is revealed, google her and decide if she's hot or not, and that will conclude my interest in the show.
Edit: And the more I think about it, the more I think the setup has been flawed from the start. I kind of wish there had been clues along the way as to who the mother is so people could try to figure it out. But this season made it clear that even the producers don't know who the Mother is yet.