Yes bring back Nintendo Sports.
Work with Konami on the PES series for Wii U/3DS, let them use Mario characters as a side mode.
Hire LeBron James and Sidney Crosby and make games based around them (basketball and hockey).
There should be a "sim mode", but a "Mario Sports" mode also in these games, so you can play a realistic style or a more aracadey style game with Mario or other Nintendo characters available.
Also make a new Punch-Out! for the 3DS and bring in Manny Pacquaio and have Mike Tyson return.
That said, if there's a money limit, my suggestion to Nintendo would be to pursue a movie license like they did with Star Wars in the 90s. Go for James Bond (currently available) or maybe make a big deal with Disney/Marvel to have exclusive Marvel games on the Wii U/3DS.
I think either exclusive Marvel or Bond properties have a good chance of selling high on the Wii U.
