Well...
*Mii: Wii Fit is part of the "Wii generic series" of games in Wii-Wii U. That would mean getting two newcomers from the same new serie, we had precedents of that with Roy and Marth, so i dont know if that is a real obstacle at all. Considering that the Icon of Wii Fit Trainer only represents Wii Fit, we perhaps see two characters of the same series being presented as two characters of different series, like Yoshi out of Mario.
Wii Fit is part of the Wii series, I agree, but only part of the series, there are many games under that umbrella. I very much doubt Sakurai would categorize the Mii solely as part of the Wii Fit series when the character has been a part of so much more, from Sports to Play to Music *shudders* to Streetpass to Nintendo Land. It would very much be like Mario being categorized as a Yoshi character.
And not to say it's impossible to get two priority newcomers from the same series, but we only got Roy as a late-into-development semi-clone of Marth. Sure it's possible, but we only got one because we already had the other and to pad the roster. It's not like Mii is going to be a clone of WFT if included.
But now the little question that i must ask you is that what does make a character "retro"? Because all this time i though that Little Mac could be considered retro, or that Wii game excludes him? Does exist anywhere a list of retro characters?
A character generally seems to be considered retro if the games in their series is limited to the NES or GB era. Perhaps SNES, but there's been no proof of that yet. Once a character has made an appearance more recent than that (as part of their series, not just a cameo), they're generally considered not to be retro any longer. Sakurai refers to these kind of characters as "classic" not "retro".
Characters like Takamaru, Mach Rider, Balloon Fighter, Sukapon, Bubbles, Duck Hunt Dog, Urban Champion, and possibly Muddy Mole, Prince Sable, and Lip could be considered "retro", among others.
Though this stuff is getting a bit off-topic.
That would hardly commence with Isaac, people have been doing it since December.
Xenoblade Chronicles has been more appraised and known than any Golden Sun game. Some company in Europe even voted it Nintendo's 9th best game of ALL TIME. As much as they both could make the cut, Shulk seems more likely.
I don't want to encourage the vs. business, but Xenoblade Chronicles has most definitely not been known more than Golden Sun. The first two games in the series
each sold at least double Xenoblade (even in Japan), and their metacritic scores (at least GS1) are about the same as Xenoblade.
Xenoblade's splash was more recent, that's why people think it was bigger.