Paper Mario would not be that expensive, so that I expect to happen. But a HD Metroid, with the intricate world design and high production values that have defined the series, would be a pricey endeavour, perhaps more so than any other game Nintendo has ever made. Look at their Wii U catalogue so far; the only one that seems like it required a big budget is Xenoblade Chronicles X. Nintendo just aren't into spending big bucks on a game.

Retro is doing a new game with a special new engine for WiiU

I don´t see Captain Toad 2 there...

I see Diddy Kong Racing U.

It really depends with Paper Mario. If they went with a SPM 2D style, it would be very cheap. If they went with a TTYD open 3D-esque world, it would be at a moderate cost (relative to Nintendo standards, anyways). But yeah, I expect it to happen as well.

I don't see an HD Metroid costing more than XCX or Zelda, honestly. Albeit, it would sell significantly less than Zelda, but it would probably be on par with XCX in terms of sales. The worlds themselves are much smaller than Xenoblade, and although they have more detail, they exist in small, compact areas. At least, if we're going by Prime 1 here (I haven't played the other 2 yet so I don't know if they've significantly opened up the areas).

Furthermore, they could go with an Other M style of gameplay which would be very linear in comparison and would be an overall smaller game in terms of length and scope.

Ultimately, there's a lot of things Nintendo could do to cut down the cost of the game. I think they shouldn't underestimate the selling potential of the franchise and if they want to go into the next gen guns blazing, they need to keep expanding on their franchises rather than keeping them locked in a basement for generations at a time. Of course, this doesn't necessarily mean that they will do what I'm saying, but I think it's in their best interest and there's a chance they will.

Pfff nop. XD

That happened one time, there is no pattern there. If something Retro has done 2 "minor" games in terms of budget and ambition and now is when they do something big. I´m pretty sure that there´s at least one more huge game coming to wiiu apart from Zelda, and they can twist the Metroid saga with something new like a good online multiplayer that increase the appeal to sell something similar to the first one, that was good enogh. And of course, later can be "ported" to the NX.

I highly doubt that. Diddy Kong Racing has zero selling power for the console in comparison to Nintendo's other franchises, or even new IPs, especially considering the other kart racer on the Wii U has already pulled its weight.

I don't think it would sell significantly more than a Metroid or F-Zero game, tbh. At least, not enough to warrant its production over the others.

Prime 2 and 3 did offer larger areas than 1, and with the horsepower leap Wii U offers, one would expect that to lead to even larger and more intricate environments. Of course, it doesn't have to, but I suspect there would be quite a bit of backlash if it was no bigger in scale/complexity than a Wii game.

And yeah, there's usually a big difference between what Nintendo should do and what they actually do, haha.

NIntendo ignoring what gamers want has been a running theme this gen.

Yes, a Metroid game would do far more for their image and draw in an audience there don't already have locked down, but they don't care, they make what they want to make, without stopping to think about what the market wants. If Diddy Kong Racing means they can reuse assets from Tropical Freeze and the engine from Mario Kart 8 to make a  quick buck, that's what they'll do, without a thought as to how it will further harm their reputation.

Ah, gotcha. I still think that if gamers got an incredible, claustrophobic and atmospheric Metroid game akin to Prime 1, most would not complain. After all, many fans seem to prefer the original, correct?

Agreed on the bolded. xD Nintendo does seem to surprise occasionally though, even this gen (Fatal Frame localization, SMTxFE not being vaporware) (both of which I knew were gonna happen, by the way ) and in the past with low selling hardware (multiple new IPs on the GCN, along with two Metroid games, an F-Zero and high-profile 3rd party exclusives like Resi 4 that no one saw coming).

Fark, not even midday and I'm already on the doom and gloom wagon.
Someone hand me my valium... XD