Square-Enix, touching on this right now real quick while I'm playing Super Mario RPG.
Be noted, I'm a huge fan of all listed.
-Random Square Enix character from smaller series - Not happening.
-People want Geno because the Mario RPG's are generally really awesome, especially coming from a gigantic series that has no huge plot development, here we are with seven grand titles that just...Blow the wall. That and he's an awesome character, but in the grand scheme of things, he only truly represents one Mario RPG and hardly has much going for him at all. Cool suggestion and all but yeah
However, granted Nintendo gets Square to participate, they
better get music from Super Mario RPG.
-Chrono = Ouch. Chrono Trigger is a fantastic game with a cult cut fanbase, however It's very similar to Super Mario RPG, popular on the internet yet not much anywhere else.
-Sora = Also generally really unlikely. The main thing is his legal rights: You have to go through Square and Disney, and when Final Fantasy characters are out in the opening having everything and a bag of chips over Sora, it just doesn't seem to link up
-Dragon Quest = Really, only mainly popular in japan, and like Final Fantasy, It has no true accurate choice, but It's surely one of the more plausible ones since DQ Sells like hotcakes over there. Slime seems to be a top contestant for here
-Final Fantasy = The only protaginists that even fit in my mind for this are Terra, Cecil, and Cloud, but even then It's hard to pick someone to represent Final Fantasy between Protaginists, so the main way to please people is go for a "Generic" And iconic figure, thus leading me to something like say, Black Mage, or Black Mage & Chocobo, or Chocobo, or Moogle, etc.
-Mixed: Chocobo/Slime would work the best If you wanted someone to represent Square-Enix well, especially considering all the facts about both.
Overall: If we're for the easiest option with licensing and pleasing people, without a doubt, something that has to do with the Chocobo or Black Mage is the best bet. That however doesn't mean the other suggestions are bad; A lot are pretty neat when it comes to Square-Enix, and overall SE Has a huge history over some things like amazing soundtracks. I honestly wish they made Dissidia cross over to ALL Of Square-Enix and put it on the PS3 instead - Now
that would've been sweet.
That being said, I think at this rate I'll be lucky just to see a Square character on the roster.