After the groundbreaking, record-setting success of Skyrim, TES doesn't really need as much publicity as people would like to believe it does. A literal JPEG of TES 6 at E3 set the internet on fire, and I can pretty much guarantee it's going to be another 30+ million lifetime seller after it releases as well.
Maybe for a Besthesda rep, not going for a mascot would make sense since there's enough human reps for them to go for, but just to prove a point Jack Frost is more of a SMT mascot than a Persona mascot. Persona itself has never at all had an iconic recurring character; less emphasis is placed on the demons/personas than in SMT and nobody is a recurring front-cover character, as the only real recurring human character is Igor who is always placed in a significantly more low-key role compared to the other characters. The closest thing we get to recurring mascot-level characters in Persona specifically is icons in certain roles; like how Morgana and Teddie are known more as non-human (or part-human in Teddie's case) sidekicks, Rise/Futaba/Aigis are known as support roles, and each protagonist is known as being the main face of each game, as it's the one you see most often.
Regardless, the points you make for Dovahkiin are good ones and anything's possible. I really don't have much of an idea in regards to non-Microsoft/Square/Nintendo reps, except for realizing that I forgot to mention Dante anywhere in my original post (which I should have).
Either way, Sakurai specifically said Nintendo picked the Fighters Pass fighters and Sakurai and his team only okayed them in a decision of whether or not they could be pulled off. There's no evidence that Nintendo wouldn't go for Geno, but there's a lot pointing more towards it being that way than not. Sakurai wanted Geno in Brawl, pushed hard for him to the point where Beware the Forest Mushrooms was found as an unused track in a Brawl datamine. It really makes me feel like it was EXTREMELY likely Square didn't want to cooperate, and Nintendo didn't want to bother pushing them to, so Sakurai had to settle without Geno. Would also explain why he went as far as making splash art for something as small as a Geno Mii Fighter costume.
Regardless, I'm a long time SM RPG fan, played the game as a kid and loved it, love Geno and he's been my top requested fighter since I started following Brawl speculation in 2007. I'm just a realist who tries to look at the signs when there aren't any direct facts present, and to me, it's looking like Geno won't be in until Sakurai has full, 100% unadulterated control over the DLC again.