Personally I'm betting that Nintendo will have Splatoon , Mario Maker and Smash 4 ready at launch as the bundled pack in games. People who don't own a Wii U will be stoked that they are getting free versions of these highly esteemed games while WIIU owners were likely going to buy the NX anyway and will appreciate not having to buy these games a 2nd time.
Zelda's more-or-less confirmed for launch, and all the reports on Smash suggest it is a launch game. IMO having more than those 2 ports would be overkill. Stagger the releases to spread out the profits.
I think this would be a good launch window lineup.
Zelda - Practically an NX game at this point. A much-anticipated game and a great way to start with a bang.
Pikmin 4 - Pretty much "done" as of mid-2015, so it has to be. It's a quirky tentpole release that will get more attention as a launch game, and provides plenty for core gamers to sink their teeth into.
Smash - "Hey, see this awesome game you missed out on cuz you didn't have a Wii U? Buy our NEW system and on day 1 you get a second chance! Already got it? Double-dip and get exclusive new content!" This and Zelda will likely be the only major launch day ports.
Retro's new IP - New system, new IP from a beloved developer stretching their wings from the first time. Can't go wrong with it.
Anything else, whether new or ported, would be overkill. Splatoon is better served by a sequel at this point considering it'll be 2 years old at the time of NX's launch. Mario Maker DX would be a great title at some point though. There's a few approaches they can take it in.
If Mario Maker is a pre-installed app, I could see them trying an F2P approach. Start off as "Mario Maker Express", and then be able to download more components from the eShop. Then maybe a full-fledged, complete retail edition later in the year? Or just do it retail-wise and ignore the app thing.
Remember that
one of the primary purposes of ports is to pad out a release schedule, to make the wait time for new games more bearable. They aren't a substitute for new games - though Smash may be the exception since making an entirely new one at this point of time just seems infeasible, and it's worked great as a service game for the past year, so they'll probably want to use the NX game as the basis for the series for now.