It likely is compatible at the hardware level but the question is will the WII U accept gamecube discs ? 

I think the next Nintendo console is going to be a handheld/console hybrid device. I think it'll be bigger than the 3DS XL, but not as big as the gamepad. I think it'll connect to your TV via bluetooth, as well as through an HDMI out. Unlike every other handheld they've ever made, it'll be like Vita as far as power goes so it can compete against the other consoles at the time of release.

Because of this, they will no longer be stretched thin as far as development goes because they will only have to develop ONE Zelda,Mario, Donkey Kong etc. at a time. This will allow them to speed up releases, get them out more often and ensure that they're of the highest quality. It'll also allow them to save a TON of money, which is always a good thing.

Hmm ... I expect that nintendo's next generation SoC will likely feature a manufacturing process node of 14XM nm from global foundries or it could be TSMC's 16nm because I expect them to release a new console by 2016

Potentially speaking it could be possible for the new nintendo SoC to have 16 cortex A57 ARM cores so being more powerful than the lowly jaguars wouldn't be out of question. 

If they do pull off this move it could mean huge savings for development costs.

Very true, and it would be nice to know. If so there are a couple of GC games I want to buy. :)

GC games will likely appear in the eShop due to the fact that the WII U is lacking a GC controller port. 

maybe......

your OP is a joke.
dev costs are up 20% according to reports on new HW
I highly doubt WiiU games are more expensive to make than any other HD console. most ports were made in 6 months.

What would it be like if they kept the same old architectures ? 

Development costs rising is because of moronic management, that seems to think the only way to make a great selling game is to pour $300 million into it, with $200 million just for advertisement.

There are plenty of smaller developers around that make games that are of equal or better quality than the big blockbuster expensive AAA games and have a tiny team and almost a non-existent development budget.

Most of the initial additional next-generation costs are due to the retooling of game engines (Which in turn requires staff to be re-trained and/or new staff), which wouldn't have been a problem if they didn't neglect the PC for almost a decade and refused to support the next generation effects that were readily available.
EA was well prepared with Frostbite if you hadn't noticed, they actually save money in the long run due to not having to license an engine such as Unreal or CryEngine.
They don't need to sink millions before/after the generations start to make games look next-gen, they were already at that level.

Thus, don't blame the platforms for costs rising, publishers are still taking home billions, so don't feel sorry for them.

It's really not hard to make something faster than Jaguar. xD Even at 40nm... Or heck 65nm even.

Nintendo can move to x86 or ARM ISA and include a WiiU's CPU for BC. Espresso is already pretty cheap and tiny even at 45nm, it'll be even smaller at 28-20nm.
If they move to ARM or x86, they'll probably partner with AMD again. AMD should be able to make whatever GPU they have at that point to handle Latte(WiiU CPU) compatibility without problem.