My equally valid take on what Nintendo is doing:
They're trying to entirely detach themselves from the competition with Sony and Microsoft... if the pillars holding up gaming are graphics, gameplay, brand and value, they've decided to push gameplay and their legendary brand ahead of the rest whereas Sony and Microsoft just try to max it all out.
So, what I'm saying is, I think they won't release a Switch Pro because it's not necessary for their business model, they don't give a shit about presenting Mario in 4k, he's solid colours with some sheen.... and it would be a further concession to the 'progression' narrative imposed by Sony and Microsoft
In summary, I don't think we'll see another Switch system, we'll just see another evolution and gimmick. Wii > WiiU > Switch, this progression is very clear across this span... they wanted to have a more interactive control input; they wanted to introduce some kind of portability of game alongside interaction without sacrificing console power; the miniaturized a console into a tablet and finally got it right. I guess the next thing they're gonna do is ... I have no idea, I'm not as creative as them, maybe it'll be a type of VR, or maybe it will be an entirely stream-based delivery system that's very convenient to carry around and can achieve - shock horror! - 1080p...