Let's put some ideas that could be used in the Mario Party U game that's bound to come out.
1. Players pass around the Game Pad when it's their turn. Their items are only shown on the Pad, as are any other vital stats. The only thing that shows up on the main TV screen is where they are on the map.
2. 4 player mini games would require each player to use the Wii-mote (Pro Controller, etc). The Game Pad displays the scores, etc.
3. 1 vs 3 mini games default to the Game Pad vs the 3 other players.
4. 1 v 1 Duels can take place solely on the game pad with each player having one analogue stick and buttons.
ZeroArchery posted... I know, I missed the 1 on my keyboard. 3DS stayed at 2.7 Million for its first year. Wii U already passed it.
I frankly haven't cared for Mario Party since 3 (though I preferred 2), and wouldn't buy a new one on any system (if I want to play a game with my friends, I'll either bring out Smash, or a proper fun board game).
One thing I will say is... either it shouldn't have online (nothing like waiting 10 minutes for someone to roll the dice, right?), or it should replace players who take too long with CPUs. And even then I feel a full game is too long for online.