This isn't really anything new for Nintendo, though. The Gamecube -> Wii -> WiiU were compatible. The Gameboy Color etc. were backward compatible with the Gameboy. The 3DS was backward compatible to the DS.
It's actually quite a gamble to introduce an entirely incompatible system. Now that Sony and XBox are just x86 with an AMD graphics card, it's hard to imagine them not being backward compatible from here on out...
It is not just about BC however, but how Nintendo will innovate and focus on the hybrid format moving forward. Also as a family of devices, every new iteration would be BC all the way back to the current Switch down to even the eshop. To date, Nintendo has never been BC for more than one generation back from whatever their current hardware was at the time and required you to use an entirely separate online store specific to the console.