Not counting original IPs (which Nintendo seem to be trying to nurture as well), these are the existing Nintendo-published franchises I could think of that don't have an entry announced for Wii U yet:
Animal Crossing
Paper Mario
Mario Strikers/Golf/Tennis/Baseball
Steel Diver
Fire Emblem
Wario Land
F-Zero
Rhythm Heaven
Brain Training/Brain Academy
Another Code
Endless Ocean
Pilotwings
Pokémon Stadium
Pokémon Snap
1080 Snowboarding
Chibi-Robo
Sin & Punishment
Metroid
Battalion Wars
Geist
There are also some other third-party exclusives that could potentially get a follow-up, like Baten Kaitos, Muramasa, MadWorld. Plus, there are the Wii U games which came out early enough that they could potentially see a follow-up using the same engine by 2016: things like Pikmin, Rayman, Wii Party, maybe a core Mario platformer.
Nintendo only need to draw on a handful of these plus a few interesting third-party exclusives in order for 2016 to be a great year as well.
If, for instance, 2016 saw the following:
Animal Crossing
Metroid something
Pokémon Snap 2 (I really hope this happens given how well the Gamepad would suit it)
Paper Mario 4
Pikmin 4
Some sort of core Mario platformer
Endless Ocean 3
Baten Kaitos 3
2-3 original titles a là Wonderful 101 or Splatoon
2-3 interesting third-party exclusives a là Rayman Legends or Muramasa or MadWorld or Tales of Symphonia
A decent selection of indie games
That would be an incredible year. It's quite possible for a year like that to happen, too - Nintendo don't need to pour so many resources into developing a new home console just yet and most of their developers should be quite familiar with how to get things running on the Wii U. A ton of indie titles have been announced for the console in the past 12-18 months and 2015-16 is probably when a lot of those will start coming together.
