I'm sort of curious if it would be almost a boon.
My thoughts: Because E.A so rarely puts their games on Nintendo systems, they aren't really in a conversation as to what makes the platform attractive. E.A's lack of Nintendo is also a common criticism of the platform, as it is a fairly solid hole in their lineup.
However, should E.A games become locked on a single platform, Nintendo not having E.A games is basically the same effect as saying Nintendo sucks 'because it doesn't get Sock Boy and Sea of Thieves'. So you won't really hear it anymore.
Of course I am aware of the argument that Microsoft would have E.A be like Minecraft and appear on multiple platforms, but given how much of a 'buy a console' the sports titles are Microsoft may have more reason to hold them to their own self instead of giving them to Playstation.
Seeing the effort EA puts into Nintendo consoles and the sales their games make on the platform, locking the games away to Xbox-platform will barely affect Nintendo. That should hit Sony in the feels though.
That said, I don't believe they lock it all into Xbox/Windows. Licensed stuff like FIFA and Star Wars probably has from the licencees the restriction that it should be put on any platform. And Microsoft does that as we can see with Minecraft. Even with cross-play.
So, in either case I see little impact on Nintendo.