There is one of two solutions to this (possibly non-existant) problem.
First, a Mario/other Nintendo series (probably Zelda) crossover, Brawl notwithstanding.
Second, make the ULTIMATE Mario game, combining elements from every TRUE (read: non-spinoff) game Mario was involved in.
Imagine: Mario alongside Geno, Mallow, Goombella, the Pixls, and Luigi as they battle the nefarious evil eminating from the dark world that was Smithy's home world, as they are aided by Princess Peach, Yoshi, Rosalina, and Prof. E. Gadd and impeded by Bowser, Bowser Jr., Birdo, Wart, and the X-Nauts.
There should be platforming elements from the original games (SMB2 included), RPG elements from Super Mario RPG and Paper Mario, and 3D platforming from Super Mario 64 and SM Galaxy.
If that wouldn't have any Mario fans frothing at the mouth, nothing would.