It's simple for me and I think most people think it in that way!
The handheld console could be what wii u's tablet controller was for it, retaining any great feauture it had, like the off-screen play, with the difference of being sold seperately, to not force people to acquire something that they don't want and avoid making an non affordable console bundle!
The home console could have a catridge slot, like the handheld console ( and by that, common library ) ! Cost curtailment plus convenience , you just put out the catridge from the home console and you immediatetely insert it easily to the handheld device, to have the on the go experience inside or outside your home! Of course home console and handheld console can't have the same power ( chasis size difference, ergo no room in the portable part for the same powerful components of the stationary part and portable part must be cheaper ), therefore the game would be enhanced and upscaled in some way, on the home console!
As for common library...
There are two risks! Firstly, MK7+MK8 have sold together 21m so far, will Mario kart 9 being one game for home console and handheld console too, match these sales? For instance if 3ds was unified with wii u and there was only MK7, despite the bigger installbase it could have the same sales as it have on 3ds alone, so no money by a 7.5m selling home console dedicated version! Although, in this paradigm, wii u owners could buy as much Mario kart 7 as to reach the same sales total with MK7-M8...
Secondly, why not only bying the handheld or the home console when they play the same games? As a result, to rob the home or the handheld console, or rather just the home console, since we talk about nintendo ;)! Solution to this, would be to make the handheld console mandatory by including in the home console bundle, albeit that would have the disastrous effect of overly high price, unless you can manufacture a strong enough hardware with low cost, so the aggregate price of the two devices would be at a reasonable level! However, gaming experience on portable console and stationary console differs a lot, hence some people would buy the home console and others the handheld console and each person could consider to buy the other one device, to play their favorite game in a different way, hence common library could eventually prove to be beneficial, add to that handheld console being a substitute controller for the home console, which could be tablet-like, wii u gamepad look-alike and keeping the dual screens of 3ds!
( the above also pertains to the first risk )!,
Of course, most of you must prefer shared library instead of common library . i.e some common games and some other exclusivites on each product, to keep the people's interest ( equal for ) in both of the consoles!
Well, the negative views are extremely and unjustifiably pessimistic...I sounded alarmist but I provided counterarguments to my own concerns/standpoints! :P
