I'm not sure about a game series, but I'd be all for Peach taking a more active role in future Mario games. Obviously being a playable character a la Mario 2 & 3D World would be a obvious, but even just having her remaining a slightly more active character through out the game would be nice. Have her remain in the Mushroom Kingdom, have her give advice on how to pass obstacles, think like Zelda's Navi, Midna or King of Red Lions for example. And maybe the finale of the game could be having a Mushroom Kingdom-lead Airship Armada assaulting Bowser's Castle with Peach at the helm, that would be a nice role reversal from the norm.
Furthermore I'd go further and say they should stop having Bowser be the main antagonist each and every game. Have him take on a more similar role to King Dedede, maybe he remains a nuisance and gets used by the main villain from time to time. But have him not nessicarily be the final end goal of each and every game, have new antagonists fill that spot at least once and a while. Hell, even if they stuck to established villains seeing some of the RPG villains or even Wario as the main villain in a EPD Mario game would be sick.
Furthermore I'd go further and say they should stop having Bowser be the main antagonist each and every game. Have him take on a more similar role to King Dedede, maybe he remains a nuisance and gets used by the main villain from time to time. But have him not nessicarily be the final end goal of each and every game, have new antagonists fill that spot at least once and a while. Hell, even if they stuck to established villains seeing some of the RPG villains or even Wario as the main villain in a EPD Mario game would be sick.