That idea could be: DS/3DS compatibility/emulation.

Since the WiiU has a 2nd screen on its gamepad, it now gives the console the hardware capability to emulate games on Nintendo handhelds. There could even be an option to use the TV (top screen) in stereoscopic mode (which I realsie is a bit ironic, considering how much Nintendo dissed 3D glasses technology). It would suddenly introduce a ton of existing portable games to become playable on the TV, and effectively dampen the game drought being experienced by the console.

I know a few people who love Mario console games, but despise using portable systems, so when a Paper Mario AND Luigi's Mansion sequel were announced for the 3DS, they weren't too impressed. They're worried that Nintendo's supposed apathy towards the WiiU could eventually drive them to become a portable only developer. Making the WiiU capable of playing 3DS games could give Nintendo users the choice of playing their portable games on the portable system, or on the TV. 

What do you guys think?

I'd like to see maybe a few more 3DS-to-Wii U HD ports. Kid Icarus Uprising HD in particular would've helped make this drought a lot more bearable especially with Wiimote controls.

I wouldn't call it the same thing, especially since the Remote play requires the console to transmit picture (essentially, it's just adding an optional screen).

Having the WiiU be able to play 3DS cartridges in some way (such as via a USB dongle or through a linked eShop account), would at least give the WiiU SOME game library, as opposed to nearly the same titles we've been seeing since the console was released...

I have an idea of what could "save" the Wii U.

Maybe Nintendo could save it by releasing videogames on Wii U.

I think that might work.

Anything could potentially be saved by one good idea. The idea just has to be good enough!

Yours is not it though

It would, but I'm talking in terms of a benefit to cost/time ratio. Console games require a decent amount of time to develop (especially Nintendo, who is very strict about quality control). Why not tap into an already existing library in the meantime?

Already posted.

TBH I want another SuperGameboy / Gameboy player etc.

Let me play Nintendo DS cartridges on my WiiU please!!!! I love DS and 3DS but sometimes I just cant stand small screens and holding something "in front of me".

I never read books my neck muscles are crippled!!!!! And I also dont use smartphones on a daily basis (maybe 2 mins a day)

So again DS U / DS Player please!

P.S.  make it more like the Super Gameboy with  additional crap like painting   and maybe some filters to make the games look less  pixelated etc.

I disagree. The games are there, hence Nintendo would, in theory, just need to give them a facelift in HD. I could play some Pilotwings for instance.

It didn't saved the Gamecube, which had a fully funcional GBA/GBC player add-on, I don't believe this would make any difference.