The majority of the responses are treating the story as if they were simply going to impose Mario upon the charming game that we currently know. If they couldn't find proper characters that possess the charm and uniqueness to match the concept, then yes, Mario would have been a workable 'plan b'.
Rather than the "thank God they didn't use Mario" reactions, the more fitting statement would be; "Thank God they eventually found such 'perfect' characters for the game!" They couldn't have nailed it any better!
I dunno, pretty sure this is all some convoluted scheme that I see the truth of - that shiggy almost sent this game to its grave with his hellbent Mario-lust /s