I'm assuming the Switch replaces the Wii U. But will the 3DS live on? I assume the answer there is yes as well, but the lines between the two products is getting really blurry, isn't it?
Part of the issue is going to come down to pricing. With a handheld each person needs their own device. If this can be kept sub $200 it's sort of a no brained. If it is priced similarly to consoles today it's a harder sell.
I am also left wondering if this could end up sold as different packages. It could be packaged as a full console edition and a handheld only lite edition at different price points.
At the end of the day they all play the same games. I bought the 2DS for my 3 kids because it is cheap, but also because it is the most rugged with it's non folding uni-body so they are less likely to break it.
I bought the 3DS XL for myself because I have poor eyesight and need the bigger screen and I'm less likely to break it.
If Nintendo does something along these lines I suspect people would buy multiple Switches per household. Based on their history it's not unreasonable to suspect that something like this is in the works. I doubt it would happen at launch since, but over time I will not be at all surprised to see different versions of this system offered.