I might also add that SMG left the story open to continue. SMG2 definitely not (
the whole Mario Galaxy gets swallowed by a black hole
), and SMO's story is over, Peach chose
neither of both
, which only leaves room for some sidequesting, but not really an entire new game. They probably could make one with the same mechanics, but the setting would need to change a bit and certainly would get a different name,
Right, story is an obstacle that could prevent a Mario game from being made. Totally. For real.
Considering that Peach has mastered the art of getting kidnapped and Bowser is the most persistent guy ever, the story merely has to feature a thought control device and Peach's upcoming marriage with Bowser is on again. Naturally, Bowser has to make it the most special day in history, so he'll travel different lands for souvenirs and all that.
And yes, it's that easy to get hired as writer by Nintendo.