Let's see...what a next-gen console should be....
1.An upgrade over the previous console--If you're going to pay for something new, it should BE something new! The o3ds vs. the n3ds is a good example of this. Even though they are "technically" the same system, the hardware upgrades in the n3ds make it a viable and valuable upgrade.
2.Backwards compatible--There is only so much space on an entertainment center for game consoles. If I'm going to upgrade from of your products to the new one, you should allow me to play games from the previous system on it, as well. This lets me replace the old instead of adding another unit. It also creates the option of selling the old to help pay for the new and encourages me to continue buying the previous gen games that may still be released even after the new console comes out. Even back in the cartridge days, they could find ways to do this (Super Gameboy, for instance)
3.Multi-functional--As game consoles have moved away from highly-specialized gaming hardware to highly-crippled pc hardware, the demand for an entertainment console vs. a gaming console has risen. The usual things people hack into a console like video players, emulators, linux builds. I know some consoles have done things like this, but it's not nearly as often as they should nor is it usually as functional as it should be.
4.Durable--consoles should LAST! It's no secret that most developers don't make money on the hardware, it's through the licensing and sales of the software. So consoles should be built to last and to exceed the average user's expectations (aka, not most of us). Problems with heating or bad wiring shouldn't be a common thing with a console. (cite: Xbox units overheating and 3ds units getting bad connections with video cables and such).
5.Resistant to obsolescence--While it's impossible to predict the future, a console should be designed so that anything that comes out around the same time is a true rival, rather than getting left behind...certainly not a lesser machine that things that came out before it! (Wii being no more powerful than a GameCube vs. the PS3 & Xbox 360, for example.)
6.Expandable--Leave plenty of room on the console for interesting expansions and accessories. I don't mean things like the N64 expansion pack...that extra memory should have been in the console to begin with! But Nintendo has come out with some great things in the past! Things like the Power Glove, Robbie the Robot, The Super Gameboy!
The Super Gameboy actually holds a special place in my heart. I played the entirety of Pokemon Red on that thing!

Why portable developers are so hesitant to add external output is beyond me (I don't use the TV out on my psp very often, but it's lovely that I can when I want to).
Well, that's my 42 cents' worth!
