I'd want a 3D Mario. One similar to Mario 64 type of format

I think every Nintendo system should launch with a 3D Mario game going forward, if not that then I'd say an open world 3D Pokemon RPG game.

If the NX is a unified platform then a huge 3D Pokemon game could be a great bridge title to run on both consoles.
It's hard to pick just one game though, because you'd assume that going with a unified architecture would basically mean Nintendo could have the same quantity of games that they'd have for both systems at launch, but they'd work on both consoles, so it's basically like doubling the launch library.

It could be both, unified to share the same software library, as the rumors suggest, but nothing's a certainty until Nintendo gives the official info on it.

A Mario-game, any Nintendo-console should launch with Mario. Might not have worked for WiiU, but still. Also Metroid.

My answer will always be open world Pokemon.

Drop that Gen 7 bomb REAL hard.

If it's a handheld, a new generation Pokemon would be best to create worldwide buzz, though Gamefreak wouldn't put it on an entirely new system I think.

That wouldn't be my personal preference, not by a long shot. In the perfect world it'd be a Zelda game, which would ensure me to get the system day 1. Otherwise I'd be more than happy with a 3D Mario, which I'm always happy with.

a new ip? anyone?

If its the fusion proyect, I would choose:

-A port of Zelda U, much like Twiglight Princess from GCube to Wii.
-A 2D Mario. Safe and marketable.
-A Golden Sun remake. Something easy to make, safe and wanted by the fans.
-A pokemon spin-off. Ranger, Mistery Dungeon... whatever.
-Two 3rd party games. They can be new titles for the system or ports of current games.

For the fanboy lulz ... Final Fantasy VII Remake.

Zelda