I'm hoping that DK gets 4 reps. The problem is, Fire Emblem has always been a series that never stuck consistently with even a few characters, especially if you don't count archetypes, and so one doesn't look as much towards series mainstays when it comes to that series, as practically every character is a one-shot. Meanwhile, Donkey Kong has always been a very interconnected series, and so Sakurai may be looking towards characters that represent the whole franchise; Of which, there are only two, as King K. Rool is not in the newer games and Dixie Kong was largely absent prior to Tropical Freeze.. That's probably part of the reason there were only 2 reps in the first place. Still, I find it likely that Sakurai has changed his mindset about that, but we'll have to wait and see.
Oh, and in case you're talking Rosalina and Greninja, Greninja is a largely similar case to Fire Emblem, as new characters are introduced every game, while Rosalina was likely a request by Nintendo, given her frequent appearances in several games. So, none of those were conscious choices on Sakurai's part. His decision to add Dixie Kong and King K. Rool will definitely be, as he's not speaking with Retro Studios, and I agree Nintendo doesn't seem to care about DK nearly as much as they should.