Neither a video game, nor a traditional LEGO set.
The LEGO tease a couple of days ago was for a new type of figure featuring our beloved plumber.
LEGO and Nintendo officially announced a partnership for the Mario series today, showing off new figures that interact. Launching later this year, Mario will collect coins by interacting with other LEGO playsets themed around the series, while playing several iconic sound effects.
Retail leaks earlier this week suggested the series would have thirteen sets, though more details are expected soon.
you don't really associate Mario with vehicles
Mario actually doesn't seem like the ideal Nintendo property to become Lego since you don't really associate Mario with vehicles or locales, which usually make the best Lego sets. A Star Fox Arwing, F-Zero vehicles, Samus' ship - those would make great Lego sets. The problem is that I just listed off lower tier Nintendo franchises that fans like us love, but lack the name value of Mario, Zelda or Pokemon. With Zelda you could probably create sets similar to Castle Lego since it has lots of locales. You could make sets based on the Temple of Time, Hyrule Castle, Lost Woods, Karkariko Village, etc.
Now Super Mario RPG would work really well with Lego. And those sets would be bought by me and other geeks pushing middle age and no one else.