At this point I just want the most bang for my buck and that means cross compatibility between the handheld and the console for a majority of titles. I buy one a game for one and it plays on both, most of the time. If that means relatively weaker console specs I'm fine with that, I don't really want to spend a whole lot on a console in the first place. I have a PC to sink money into.
Ideal scenario for me is you have a capable handheld priced $150-200 tops and then a console at $250-300, better have a really great game bundled with it in that $300 event, hell even at $250 they should bundle something catchy.
More importantly though, you'd only have two divisions of games. Those that work on both platforms and those that only work on the console. Games designed to run on both could have added enhancements when played on the console, but not required, well besides basic IQ improvements. Any game that only works on the console though would be playable via streaming on the handheld like the Wii U gamepad off TV feature, Nvidia GameStream or remote play on Vita.
For me this is key. I like handheld gaming a lot. The 3DS has gotten a ton of great games and I use it all the time. Wii U though has only a few I really want to play and as of right now none have pushed me to get the system. Only Zelda at this point will do that. But had the Wii U been cross compatible, where I could have played my 3DS games on the big screen with better resolution and IQ I would have been all over that and bought it years ago. It's a value added feature. People can talk about lost sales by not having multiple game versions for both devices, but from my perspective that's negligible compared to potential sales from those like me who have completely abstained from getting the consoles at all, let alone whether I bought both MK7 and 8 or Smash on both systems. Great they'll lose on that double dip opportunity, but now I'll actually be buying the console system, plus console only games and other crossplay games because I can play them on either of my devices depending on my mood. For me that would be a major incentive that would bring down my threshold of whether to buy a game or not cause it will feel like I'm always getting two games for the price of one. When in reality that's only the case for very few titles traditionally.
Plus you'd have other simpler stuff like using the handheld as a controller for the console, especially if they toss the Gamepad type setup so those who like it could still effectively have a second screen experience again allowing you to access menus and look at maps via the handheld without pausing. In the event they do retain a gamepad like controller the handheld could then act as a ready second controller allowing for interesting co-op/multiplayer that the Wii U never got to explore.
