A serious mario... hmm..
I don't know how you could possibly make a serious mario, considering that the whole idea and concept of mario is that of a fun-loving, fat, jolly, comical italian plumber. Nintendo uses "mario and the gang" to get kids to buy their products. He's not exactly a dynamic character. Nintendo would need to flesh out his personality and give him deeper motives, a past, ambitions, hopes, etc.
It could, however, be quite innovative if it was ever made.