Oh i think its quite easy to determine how much MP gamers are out there. Well...depending on the gen. THe thing about Ninty systems and im just going to say it they miss a LOT of 3rd party games period. its been that way since N64 and its that way with Wii U and I dont see that changing. Now with that being said their is a conditioning where you HAVE to get another console or you miss out.
You know, whenever the discussion of Nintendo and 3rd parties comes up, a vital element of it gets usually (and conveniently in some cases...) ignored... Handhelds. For a lot of Nintendo fans, handhelds are part of their steady gaming diet, with not only plenty of support from Nintendo themselves, but also a ton of 3rd party support. And for anyone that plays Japanese games, a Nintendo handheld becomes just as much of a must have as a non-Nintendo console, specially DS and 3DS. Do Nintendo fans in general need more than this ? I don't think so... And if you do, there's also PC to consider here, or those who just play other consoles through friends and such.
Basically, I'm skeptical of Nintendo fans being more prone to get another home console than other gamers, and I believe it's more of an individual choice than anything, with factors such as gaming budget, personal taste, and time to play games being crucial here. Hardware sales can indeed add to your point when they favor other platforms, but then again, the same could be said of Wii, DS and 3DS, yet people usually talk about there being different demographics when it comes to those... So, which one is it ? Different demographics or multiplatform gamers ? The truth is probably somewhere in the middle, and without actual data, we can only speculate.
I'm also of the opinion that the issue gets a bit overblown in general... I mean, sure, too many 3rd party "AAA" games skip Nintendo consoles, but it's not like there's nothing to play... You still always get a good share of exclusives and ports, like Sonic, Monster Hunter, Resident Evil, Tatsunoko VS Capcom, No More Heroes, Lego games, Just Dance, ZombieU, Watch_Dogs, Project Cars, Harvest Moon, etc... So, it depends of what kind of gamer you are.
Think it comes back to Ninty vs. video games. Is Smash supposed to be a celebration of Ninty history? Or game history in general? Becasue IMHO it doesnt matter if Alucard, Simon, Soma or whoever shows up. Its stopped being strictly about Ninty the moment they announced Solid Snake in the game. But maybe they are trying to close pandora's box. Hell as soon as they said they would have 3rd party characters it stopped being about just Ninty.
Well, as much as I think Snake was not the best choice for Smash, he still arguably had some relevant history on Nintendo platforms, so he's far from being the worst choice. It would've been far worse if someone like Cloud got in for example, without ever being before on Nintendo. So, as I said before, I think the requirement should basically be to have a significant history on Nintendo platforms and be a good fit for Smash. You can be a bit more selective in the future and be certain that whatever character you choose has a good reason to be there, with a strong bond to Nintendo in one way or another. I would definitely disagree with using Snake's case as an excuse to fully open that pandora's box and just let any popular character in... But of course, it's not up to me anyway...
In any case, Smash will always be about Nintendo first and foremost, and Sakurai makes this quite clear when he says that the likes of Mega Man are special cases, limited from the start. Whoever gets in in the future, it will not change that.
The other possible Konami reps (Simon and Bomberman) are also worthy characters in their own right, but what chances do they have against a veteran?
I'm not sure what you mean by "veteran" here... If you're refering to his long history, let me remind you that Simon and Bomberman have existed since 1986 and 1983 (1985 on Famicom) respectively, being among the first 3rd party characters on Nintendo platforms. And Bomberman in particular has appeared on pretty much every Nintendo platform since then...