I'm guessing Fifa and or Madden (for the US market)...

I have a feeling it's Plants vs. Zombies garden warfare.

Actually, it doesn't sound that crazy. Splatoon proved Nintendo fans would buy unorthodox cartoony shooters if given the chance, so they can push it that way. Maybe Gearbox will bring Battleborn following that same logic.

I'd love for it to be Battlefield 1 but I'm shure that's not the case, ME is already out of question since the developers confirmed they won't be porting it to Switch (unless someone else does it for them...)

I know Nintendo needs third party, bu do they really need to have third party games just to have third party games? I mean the Wii had a shit ton of third party.

Doubt that, since Battleborn is pretty much dead after the success of Overwatch.

So much this, keep in mind that these exist

And consider that the Xbox360 was released when that Psone game dropped and the PS4 was on the shelves when the PS2 Fifa game was released.

Nintendo needs 3rd party games if they want to attract people from outside its traditional userbase, but that's not the key here. The key here is that 3rd parties are really weary about releasing games on Nintendo systems, and they want to know which kind of games would sell well to avoid any kind of risk. Look at Ubisoft still releasing Just Dance games on the Wii-WiiU, they know it will sell enough to justify it, so they do it. Companies with games similar to Nintendo's may use established successes like that to release their projects on the Switch.

Battleborn didnt seem to do well on any system. Why would Battleborn attract people who didnt buy it on their system of choice?

If they are going to make it FTP, maybe to try it on a platform that has not had that many experiences with online FTP.