They will if they want to very successful launch and to bring the attention of industry, they most likely want that Switch become must have because of great games out of gate. I think Laura also said that Mario and Zelda will be launch titles.

But they will need something very big for the holiday season.  New Mario Kart, Smash or Splatoon games won't be ready for late 2017, so 3D Mario is what's left.

They have to think about having games after the launch as well. Thats just as important, if not more. Having Zelda and some smaller ones and some big third party games, with Mario announced for the holidays will be good enough.

I had figured as much, it's good to have clarification though.
I've seen people assuming that they were full-on sequels just based on the wiiU engine to save time, or even just concept mockups thrown toghether last minute for the trailer.

Offcoures, its not like Mario is their only big game, they will most likly have some new game ready for launch also, Pokemon will almost certain be ready for 2017, Retros game, Next Level Game project,  posible Pikmin 4....while they will use old Wii U ports to fill holes in schedule release plan, they will not use ports of old Wii U games like main launch games.

I hope ports of recently released games isn't all what they've been working on during the WiiU's last drought.

Zelda is confirmed.

Can't think of not releasing a new Splatoon version for launch too as this is one of their biggest active communities which might switch instantly.

Im not saying there won't be new titles at launch but Smash has a specific audience. I don't think it would clash with single player games like Mario or Zelda. I suspect Nintendo will have a more casual party game at launch too, but again I don't think that would clash with Smash.

I'm not saying that will not be Smash or some older Wii U port on launch, I am just saying that they will not be main launch games.

Also there was a rumour from a reputable source that 3D Mario wasnt running smoothly enough for a September reveal. I personally thought what they showed looked identical to a Wii U game for a titles supposedly build from the ground up for a 3x more powerful system. Makes me question how far into development it is. We'll have to wait til January to see.