This is me simply re-writing what everyone else has already figured out.
In SLS, when Kurt confesses his feelings for Blaine, one of the two brings up ‘When Harry Met Sally’, and Blaine later says 'Don’t they get together in the end?’. Now it’s been re-hashed to death that originally Harry and Sally were not meant to get together, so I wont go into that again.
Now we’ve gotten a Tweet from Brad saying that 'Blaine’ is based on “Blane” from Pretty In Pink, now I will say I’ve never seen the movie however every Brat Pack movie had the same basic plot (in much the same way every romance book ever written is the same), and the original plot line called for Andie to get together with Duckie, and not Blane, but they changed it because it’s what the studio wanted. Then a year later they re-did the movie with the ending they wanted.
Now, think back to Paley. I don’t remember if it was Ian or Brad who said they listen to the fans but they don’t write the show based on what they want. I’m going to take this to mean that; yes they are aware of the fandom. Yes they do throw the fandom a bone every now and again (Puckleberry in the B9) which is exactly what I think Blaine/Klaine is. It was the writers looking at the fandom saying 'Well, we’re not really doing anything with Kurt’s love life until New York anyway (I firmly believe it was always meant to be in the last couple of episodes of the season that we learn about what’s going on with Sam) and the fandom wants a Klaine kiss, lets just give it to them.’
So the two 'canonly’ given plot lines we’ve been given to base Klaine on, WHMS and PiP, both had their endings changed because of outside influences. The writers have told us that they don’t change major plots to pander to the fans. Which I guess says one of two things, 'Klaine was always on, and anyone who thinks differently is delusional’, or it means 'We gave you guys all the clues you needed to see that Klaine wasn’t the direction we were going in, you just missed them. Kurt and Sam are fucking in New York, so sorry for your creys.’