Well, looking at the whole thought of the Peachnappings thing getting stale, even though 3D World has changed it up, here's what I would love to see the story change:
It would start by Mario and Peach finally settling down and becoming the king and queen of the Mushroom Kingdom, but still giving Peach all the powers of a Monach of the Kingdom. Bowser would seen purely enraged, as he attempted to capture Peach one last time before her Toad army, trained by Mario to actually douse his fire-breathing abilities, chain him up and sapping him of all of his power, and then encasing him in stone for eternity. Years passes, and Mario and Peach have two sons: Azure, the older brother, and Vert, the younger brother. They are visited by Luigi, who has been betrothed by Daisy, but then, yes, Peach and Daisy gets kidnapped, but it's by the hands of the fully matured Bowser Jr and his army known as the New Koopa Republic. So, with Mario's wife and Luigi's fiancée captured, and with the army of Koopa thugs loom in their paths, Mario and Luigi, along with their sons, sets off to save them. But what if it's a diversion for the army to bring back Bowser from his stone prison?
So, what do you think of the story?