Just thought I would give a year by year rundown of total Nintendo hardware this generation in an attempt to see how much a unified handheld/console next-gen could realistically sell.

2011-13 million

2012-16 million

2013-18 million

2014-13 million

2015-??? (10-11m)

2016-??? (6-8m)

2017-??? (3-4m)

2018-??? (1-2m)

Total, 80-85 million

Assuming that Nintendo's unified devices sell roughly this much next-gen, would that be a sustainable market for Nintendo?

1-2 Million by 2018? I don't think that's realistic nor sustainable to begin with...

One problem with a unified console (I assume you mean both in one) is that a likely outcome would be the thing being too costly to sell a lot, or too weak to be appealing. Both of those factors could affect sales. If done right, though, it could help shave off waning interest on both fronts and combine them into one profitable platform.

Clearly their successors will be out for 1-2 years by 2018 and will be around the time Nintendo officially discontinues 3DS/Wii U, retailers will not likely just be selling off their final units.

80 million is good, but not for the Wii U or 3DS due their development and production costs. Expanding and increasing the consumer base should the agenda heading into their next console. That being said, hopefully 80 million and then some is the key.

No, I mean 2 seperate devices that share the same architecture, operating system, online infrastructure, software library and allows cross-buy/cross-save.

A handheld that is a moderate improvement over Vita in terms of specs, similar to 3DS compared to PSP. A device that can handle Wii U level visuals on a small screen and lower resolution.

A console that is a moderate improvement over Wii U in terms of specs, similar to Wii compared to GC. A device that can handle Wii U level visuals with some extra effects and a higher resolution.

Since these devices would share so many similarities in terms of hardware, it would be easy to scale games up/down to one another and since they wouldn't be releasing completely seperate games for two completely different pieces of hardware, they would be able to significantly improve their software output.

Either of these devices could realistically retail for $199.99 at a profit in 2016/2017, assuming they don't go for extras that jack up the price (3D, Gamepad).

I don't see them driving up dev costs by much, similar to how Wii didn't have exceptionally higher dev costs than GC. Also Nintendo has been making more low budget digital titles lately and I assume they will keep increasing since they will be increasing their software output with this approach. So Nintendo will be making a nice mix of low, mid, and high budget titles for their devices.

I agree the goal shouldn't be 80m but they should definitely make it so they are still profitable with that number.

I think they can sell more combined in 2015 than 2014

Even with two devices I feel like the same issues would apply.  People are already unhappy with how weak the Wii U is; making it two entire generations behind the competition is going to make people furious.  And buying both systems would still be a big investment, yet you're investing for hardware that isn't that great.  I feel like it's a really tricky situation--not impossible, but extremely tricky.

Yes u are right that some people feel Wii U is underpowered but mostly it's underpowered for how much it costs. It's $299 compared to $349-399 for the competitors which are much more powerful and have more features. If it were more like $199 compared to $349-399 than the underpowered claims wouldn't be a prevalent because a device that costs roughly half as much isn't expected to be as powerful.

The main issues for Wii U, in my opinion are, it's high price point compared to previous Nintendo devices, low software output, and lack of effective advertising. Releasing a $199 console fixes the price issue, unifying software development increases the software output, and hopefully Nintendo can improve their marketing as well. A device like that is a much more appealing product than Wii U currently is.