Indeed, there was the earlier idea of the SCU dock with the 1060-derived GPU.
It may well be possible that Nintendo's plan is that they will knock out the 'upto 1080p' Switch as standard [it's still after all more powerful than the WiiU), with the portable side of things being consistant for battery reasons etc, but with a dock upgrade to allow 4K play/processing upgrade when docked later.
A consistant argument I've seen is that the reason Nintendo opted for a Maxwell-based Tegra chip is because A) Nvidia did them an absolutely stunning cost per chip for the unit, and B) Nvidia couldn't have a Pascal orientated Tegra available in the numbers they needed soon enough; B may have also played into A as Nvidia have been rumoured to have been desperate for a hardware deal.
Part of said deal may have been that Nintendo would recieve the hardware for a working Switch device now, with Nvidia to provide them upgrade SKU's for a '4K' dock at a later date. Nvidia will have been working with Nintendo on the APIs and hardware, so it wouldn't be unbelievable that part of the deal involved Nvidia having to ensure that the new Pascal hardware slot in would work well with no/minimal dev hassle, sort of similar to how PS4 devs have some 'profiles' for the Neo.
Recently Reggie Fils-Aime stated Nintendo would provide 3rd parties everything they need with the Switch, and providing an augmented home experience later on, with an SKU with increased processing may well tie into that, as that will allow the 3rd parties the power they want for easier ports, but they can begin getting used to the APIs and platform now.
As it stands, it would also be a semi-smart move on thier part; they can sell the standalone Switch unit to Nintendo diehards/wider fanbase with the standard unit (who wouldn't want to pay more for more powerful hardware) and enable the market to move on from the WiiU which has not been an overall sucess for them, begin to consolidate the home and portable dev teams around common hardware, and then try to recapture further market later on with an augmented base unit/home console segment ala the PS4 Neo, which they could either release as a bundle (Switch+) or as an aftermarket upgrade. If they did indeed go with something close to a 1060 GPU, that would be more powerful than anything in any of the current consoles, especially if the enhanced dock contains additional CPU/RAM resource.
My feelings are they want to get away from the WiiU as quick as possible. You can only hope that if some of the younger bods inside Nintendo are having more input on the Switch, something like this may indeed be in the pipework and they aren't being entirely deaf to the wider 3rd party dev betwork and international markets.