SoldierMellark1: I'm not saying Johanna and Gale as a couple isn't plausible, but statements like "good luck to him and Johanna" remind me of others I've seen around the fandom, that imply that this pairing isn't just speculation, but established canon fact. It reminds me of how so many fans assume that Cato and Clove were romantically involved, to the extent that many criticized the movie for showing Cato getting cozy with Glimmer instead, insisting "The movie got it wrong! In the books, it was Cato and Clove!" I can just imagine some fans reacting to MJ the same way if they don't show Gale and Johanna in a liplock at the end, that the movie somehow departed from the book.
Ivana points out some solid reasons to NOT support this pairing. Personally, I'm not sure why it's that popular. I guess many people see similarities between Gale and Johanna, as they both seem to show a tendency to be vengeful, ruthless, and deceptive...but those are all pretty negative things to have in common, or base a healthy, lasting relationship on. (Maybe some fans see them as a grown-up version of Cato and Clove?)
Also, while I've read many Gale-Johanna stories, many seem to portray her as just a sexy, "bad-ass" girl and ignore her background as a victim of torture, as well as the likely murders of her loved ones on orders from Snow, in light of her comments in CF that "there's no one left I love". Johanna is a deeply wounded woman, and I'm really not sure Gale has the capacity to understand and support her. I can see them having a fling, but a serious relationship that inspires Johanna to leave the district we know she's homesick for, that leads to marriage, kids, etc? Not saying it's impossible, but I don't see it as that plausible. Gale certainly provides little emotional support or comfort for Katniss in MJ.
I suppose another reason for the popularity of this pairing, is that is neatly pairs off two significant characters whose post-war lives are left vague by SC. But to me, that just seems TOO "neat", or "cheesy", as Ivana would say. It doesn't seem to be at all in line with the rest of the ending, which is far from that, and manages to be open-ended and hopeful, but not in a cheesy way.