Do you think Nintendo would agree with the idea, or they think it would damage the Smash Bros franchise, because it would no longer be the only fighting game with Nintendo characters and therefore it would make Smash Bros less special?

Nintendo could have Smash Bros, Nintendo vs Capcom and Pokken Fighters (for 3d fighers)

No thanks, I'd rather a Nintendo vs Playstation.

I wouldnt mind it as long as Sakurai is in charge

That already happened. Smash vs. All-Star, it was a rather lopsided battle... :p

I meant nintendo characters and Playstation characters in one fighting game.

I think Nintendo fans care more about Capcom characters than Sony characters, probably the same goes for most videogame fans. Capcom must be the company with the most recognizable mascots after Nintendo.

I know. That's why it was tongue in cheek.

I like the idea but i feel that it would hurt the Smash Bros franchise. Some might prefer a NvC game over Smash 4 due to the probability that it will be more technical and competitive, making it a "better" game . However, I don't think the average Smash fan would be very interested with a standard fighting game . The appeal of Smash is that it's a very easy game to pick and play with friends.

I would also find it difficult for Capcom to put their own spin on Nintendos characters since most of the moves from Smash could be transferred over. Character roster would also be difficult. Unless Capcom puts the entire roster of Smash 4, there is going to be backlash from some Nintendo fans if a character from Smash 4 does not appear in a NvC game

I think Capcom is more willing than Nintendo, they have said that http://www.cubed3.com/news/15105/1/ono-nintendo-x-capcom-ask-sakurai.html, and the game would surely do well because Nintendo fans will buy a game with Mario, Link and Samus.

Fighting games are niche and it doesn't take a lot to sell more than your average Marvel vs game.
Look at this http://www.vgchartz.com/gamedb/?name=marvel+
Even on Wii U they couls easily sell much more than Marvel vs Capcom 2 for PS2 which had an install base of 150 millions.

I think Nintendo doesn't want it because it is a risk to Smash Bros, I imaine they probably want to have Smash Bros as the Nintendo 2D fighter, and Pokken fighters (if it exists) as the Nintendo 3D fighter.

Seems like the roster sizes would be a bit lopsided...

O/T: It could happen. Stuff like Hyrule Warriors and sponsoring Smash tournaments makes me think that Nintendo is starting to loosen the strict control they've had over the IPs over the years. I can't say I'd bet on it happening, but with Marvel taking the rights to fighting games for itself back, Nintendo's as likely a partner as any if Capcom crossover fighting games are going to continue.