It's possible someone's already said this, but bloody hell - I've been putting off watching the season until it was done and I could watch it in quick succession, and then I see this topic at the top of the active threads thing that shows up on the main page. Would it be at all possible for you to change the name of this thread to NOT be super spoilerific, or at the very least, preface it with SPOILERS and enough text so that it doesn't jump into my brain as I read down the main page?
Since I'm here, thought I should jump in and say that it sounds like a good idea, depends on how well it's executed, which I will assume is not too well, just out of the blue, but will probably still work for me as long as they play it right after skipping over the actual development of the relationship. It would also be fine if they didn't want to go for romantic entanglements at the end, but given that setting a possible happily-ever-after scenario thematically works best for the series (I'm assuming that's where it's going), the romantic element helps sell/ensure that for most folks, so it probably makes the show work the best for the most people, so I'm good with that.
And as for comments I've seen regarding lesbian couples in animation, while it's true that in Japanese animation there's a well-established history of that, I'm not familiar with it in western animation, and I think that what Korra and Avatar have done in this case and in general is pretty outstanding for their genre and medium.