I think the other companies are actually trying to run Nintendo into the ground. By doing all of this it really is hurting them. They might be trying to once and for all get rid of them as a whole.
It's plausible, but stupid. Nintendo is still conservative with their money and will be around for a long time even in the unlikely chance that they have to find alternatives. Sony is bankrupting themselves, and the Xbox is a significant drain on Microsoft's resources.
I'm not going to put my money towards a bet, but I expect Sony to eventually be forced to bow out of the console race or neuter the PS5/6/7/whatever to stay solvent. Microsoft I think will be restructuring the Xbox brand so that all's left is a version of Windows 9 that is optimized for controller navigation.
Windows 8.1 is pretty close in terms of interface, just that both Microsoft has to allow Steam games better integration into Metro and programming guidelines need to be updated to support controller navigation. I can actually see this happening easily. Xbox One games can be ported to Windows and back with minimal difficulty, and opening up Xbox so it's just a tweaked version of Windows (like how Windows 8 was designed to work on both touchscreens and desktops - only less drastic this time) could possibly make Steam machines redundant. Microsoft would have to work with Valve to make Steam's big Picture Mode seamless with the rest of the interface though.