Looks like the controls of the tablet controller are removable and the screen goes in the front of the console, which would work as a second screen sort of.
I don't see why this couldn't work. What if they are all sold separately? Console (with normal controller) could be $100, SCD $250, tablet controller $150. You could then buy just the console and SCD for $300. You could buy the tablet and SCD for $400. You could also buy all 3 for $500.
This could work for Nintendo, but to include the hardcore gamer, they would have to announce that by x-mas 2017, they will have an upgraded SCD that goes toe to toe with Pro at the very least. I wouldn't be surprised if both the Nvidia and AMD SCD's are sold, one being cheaper, the other more expensive and more powerful. That would solve all of Nintendo's problems right there. They did say way back when they first announced NX, that they were looking to be able to build a system that you constantly want to upgrade in certain ways. With the Pro and "Scorpio" upgrades, as well as the rumors of removable sticks and buttons and face plates, this could be true. It should pull in a lot of third party devs, and would be a great way to keep gamers up to date in the Nintendo ecosystem, and give them personal choices of how they wish to game.
Imagine if Nintendo started selling those backpacks with li-on batteries in them. You could have the SCD and the pack charged, plug the SCD into the pack USB as a power source, and game on the go at the highest quality for extended periods of time.