A proper Metroid at launch would go a long way. The most obvious choice.
I wouldn't mind finally getting a new f zero, but I guess Fast Racing Neo will have to fill the void because Nintendo don't care.
Personally I'd love the Custom Robo to series to come back, but if F Zero is a pipe dream, than CR is never in a million years.
I figure Star Fox is off the table since we are already getting one next year.
New Fire Emblem. Though that probably won't happen since we're getting fates soon and that SMT crossover.
Some new IP that's a major game, not some small eshop download (we need big stuff).
Be nice to see Monster Hunter grace a Nintendo home console once again.
Well, I wasn't gonna bring it up myself, but...
This would totally justify it for me (big surprise, right?). NX is rumored to be handheld/console hybrid. MH3U was on Wii U and 3DS, and you could transfer save data between both. I feel like this would be the perfect for MH since it wouldn't necessarily splinter the player base like 3U did. Heck if it ends up being MHXU or whatever the next MH that comes west, that would be phenomenal at launch. MH is one of a few 3rd party games Nintendo fans seem to receptive to. (Slightly unrelated, but I wish Nintendo would just buy Capcom already, or at least merge. Quit with the foreplay you two.)
That all aside, there are two main things they should have learned from the Wii U (I hope):
1. You can't just throw a 2D mario on there and call it good (especially since Maker is out)
2. ADVERTISE YOU FOOLS
I remember that there was a time when topics were created solely because someone saw an advertisement for the Wii U. Wasn't that hilarious(read: sad)? I expect the NX to launch and sell much better than the Wii U, if they have in fact learned some things from this past gen.
That's my two cents.