Bold: That can be said for them two in a way. But thats a problem they would haft to overcome and deal with. Its just the lack of Blake and Yangness that we have nothing to base our conclusions off of as solid theories or even proof. Honestly, I think they counterbalance each other pretty dang well as they are pretty much opposites when it comes to certain things and just basically have polar opposite personalities.
For example: Blake loves reading books! But Yang would much rather punch a book into the wall and watch it burn. But if Blake took the time to show Yang the meaning of books (however the fk that happens) then maybe Yang would understand too. Granted thats not in any way accurate to the show or characters really, but hopefully you got where I was going with that.
If I had to say one way or the other, I'd go with Sun for a couple reasons. I personally put more stock in those traditional/tropey hints because they feel like they come more naturally/are more character-driven than vague "themes". Sun feels like he's in a better place than Yang is right now Blake-wise. I also just feel like Sun and Blake fit together better than Yang and Blake do. My dislike for her character aside (horrendous decisions, personality and background are super..."stereotypical girl oc", though of course not actually being one), she seems to react happier to Sun, and Sun seems far more accepting of her flaws. While Sun seems to accept her for who she is and quickly forgives and forgets her actions he disagrees with, Yang always seems to want to push her, and is accordingly crushed when Blake lets her down. Yang seems like she'd just get hurt a lot more being with Blake, and Blake would feel a lot worse because of that. (I can't wait to see them hopefully address Blake's reason for leaving being "personal issues" when she had it the best in her team, and the fact that she didn't actually come back for them.)