EA and Nintendo don't have at the moment the best of relations. After all the problems with EA trying to push Origin on the WiiU, and boycotting the system when they failed, the lack of EA games has been pretty bad for the support of Nintendo consoles. With their almost monopoly on sports licenses like FIFA, Madden, UFC and others, their support is important to satisfy that part of the library. They also have other titles, but let's focus on the sport games.

Nintendo has also a lot of experience with sports games, but not in the same way. The Mario sports are wackier and simpler versions of the sports, and Wii Sports games are all focused on motion controlls, presenting a simplified gameplay to acomodate those controlls. And a lot of people like sports games, the lack of them on a system is a really big hole.

EA Sports games are usually critizised due to their full-priced annual releases with barely any updates, and sometimes glitchy launches. And yet they sell wonderfully everytime. Nintendo could take the advantage of that and make a very polished sport experience. The problem is the brand. EA has the licensed brands of FIFA, Madden, UFH, and a lot of sport celebrities, that alone sell millions of games. Even if Nintendo could develop a strong game, they would not have the same strenght (they could use miis as players, but again, the problem is on the license) to market the game.

Could Nintendo actually make a serious sports game to fill the gap FIFA and the other games leave if EA decide they won't come back?

EDIT: I'm not talking about Nintendo outselling FIFA. That is impossible, considering FIFA is on every system known too man BUT Nintendo's. I was thinking this more in the lines of like Nintendo needing COD, to attract multiplatform buyers rather than to satisfy their own userbase.

I think they should have pushed to try and secure PES on Wii U. It would have zero competition and most likely sold ok numbers.

I don't think so, without the licenses for using the image of all the players it's almost impossible to make a realistic sports game...

I just realized how terrible the situation is with the football videogames with EA on one side with FIFA and Konami on the other with PES...

no, football fans these days buy because of the Name FIFA on it. PES is the best example, its actually the better franchise and it always was but it ended up failing so more casualized the console market has become.

True, I didn't even remember PES. Why isn't it on the WiiU when it would literally have ZERO competition is a mystery.

They already did: Mario Strikers. It's up to them to updated it, add a cool online mode and promote it. I know OP doesn't count it, but since Nintendo fans needs are different, I still consider this game as a contender. :)

If they invest on it like they did with Splatoon, I'm sure it can be successful.

PES is owned by Konami, and as of now Konami is worse than EA ...

I would love a new Strikers with online multiplayer. I was thinking this more in the lines of like Nintendo needing COD, to attract multiplatform buyers rather than to satisfy their own userbase.

No, Nintendo's core fan wouldn't support it and the football fans would simply go for Fifa. Nintendo would need to re-establish themselves as popular with the mainstream before they could even consider this. However if they were popular they wouldn't need to produce their own because EA support would be a given. There's very little incentive for any of the big three to try and compete with Fifa or any other mega sports franchise.

Ah, ok. In that case they would really need to bring a new IP indeed. I'm sure they could do it, but would it be "good" for their third parties relationship? That is, if they really want them on their next system.