I think Sony is basically out. Vita is just not doing it.
Nintendo however is still in and if they are smart they will do as follows:
Nintendo Game Player: Successor to the 2DS, and is a small handheld with a single touchscreen and dual analog controls. $99
Nintendo Game Tablet: Successor to the 3DS XL, and is a large tablet with a single touchscreen and dual analog controls. $199
Nintendo Game System: Successor to the Wii U, and is a microconsole with dual analog controller with a touchpad on it. $199
The important point about these three systems is that they for the most part would share the same library of games and would have the same hardware and OS inside, and to further this, Nintendo should have an account system similar to the PlayStation and Xbox brands and should allow support of something like Unity. Any game made for the Player would also work on the Tablet and the System as well and even in regards of physical format, Nintendo should use something similar to 3DS Cards. However, this is not to say that the three would be completely interchangeable in that there are some things which the Nintendo Game System would do that the others wouldn't, namely if one wants single-screen, local multiplayer or to use accessories other than the default controls, they would need to buy a System. However, Players, Tablets, and Systems would play ad-hoc and online against each other with no trouble since they are basically the same system inside and out. The Touchpad on the System's controller would be how one can play games designed for touch on the System. In this way, Nintendo can continue the ideas that the Wii U started. I think it would be end up with decent enough sales and show that Nintendo is determined to make an iOS/Android-like software platform rather than rely on differing hardware and software. The names I suggested are intended to invoke both the Nintendo Game Boy and the Nintendo Entertainment System while also being clear on what type of hardware each device is.
I think you've got things basically right. This appears to fit Iwata's description of his plan. I don't know if it will work, but it think this is what they're going to do.
Exactly. The kindle is so damn good at what it does, and so well-priced, that it exists even when almost everyone has two or more devices to read books on.
No reason why the next set of handhelds can't do the same. Right now they're too expensive and unwieldy, even though the 3DS is at least close to the right price.
This is a good point. When my wife lost her kindle, I suggested replacing it with an ipad, but she just wanted another kindle. Maybe there's room for a dedicated handheld to command similar loyalty.