Yeah long term the "two seperate portables" wouldn't work. Two Nintendo platforms only work long term if the "console" is a home ONLY device. Nintendo's never simulatenously had *long term* success with two seperate home consoles or two seperate portable game machines.
Another portable Nintendo platform has extremely limited appeal. Yes Switch is more expensive, bigger, less battery life now, but all those issues can be addressed simply with time and a die shrink to 16nm. So your whole theory "yeah but it's not a handheld" goes down the toilet in about 18 months when Nintendo will likely start releasing Tegra X2 variants of the Switch and the price is $50-$80 cheaper than it is now.
The "Nintendo fans will buy it, Nintendo fans buy anything" logic doesn't hold either, many Nintendo fans opt not to buy 2 Nintendo hardware pieces. The Wii/DS were successful but the Wii had a lightining-in-the-bottle motion control fad that the DS didn't to drive sales for about 4 years.
Most Nintendo fans did NOT own both the GameCube and GBA (as evidence that 80% of GBA owners did not buy a GCN). Same thing is true of Wii U and 3DS, most Nintendo fans said "nope" to Wii U.
