Possibly, but the gain for Nintendo is also potentially huge. Switch as it is, is getting barely any AAA 3rd party support due to it's low specs relative to PS4 and XB1, and that will only get worse once PS5 and Scarlett release and graphics advance even further, xCloud would allow Nintendo to continue offering AAA games on Switch into the early years of next gen. Nintendo and MS could form a symbiotic relationship with MS putting some of their exclusives onto Switch and AAA 3rd parties onto Switch via xCloud streaming, while Nintendo returns the favor by putting ports of some of their games onto Xbox.
I understand the idea, but I won't get my hopes up for this. Even if they, say let us play Banjo-Kazooie and/or GoldenEye on Switch.
Also, another possible benefit for Nintendo in such a partnership would be that MS could help them get their online service up to snuff, since it is kind of sad right now. MS has alot more experience with online.