Real response: Nintendo will want to rally their support for their platforms. They already have history with them, thanks to Rareware, and nostalgia plays a huge role for Nintendo in building an audience for any platform they release. Banjo and Perfect Dark's return to a Nintendo machine will create headlines. A new Donkey Kong game from third party studio, Rareware (though they are a shell of their former selves), would spark headlines. Master Chief in Smash would have more exec support, as they won't be propping up a competitor's machine for that inclusion (Minecraft is already on Switch and the Japanese audience for Minecraft are playing on Switch/PC).
Microsoft game's are largely engaged from an American audience. The USA is the world's biggest game consumer, and the only big pie Microsoft really caught on with. There will be a Nintendo response. Maybe not so much in how they develop their hardware, but I would anticipate even more marketing collaborations, cross promotions, and the like.