Shigeru Miyamoto says he'd like to keep character revelations from The Super Mario Galaxy Movie intact going forward into future games in the series.
Spoilers for The Super Mario Galaxy Movie to follow, read at your own risk.
In The Super Mario Galaxy Movie, some major changes were made to the canon of the series. Notably, Princess Peach and Princess Rosalina – who have barely any interaction in the game series – were revealed to be sisters, both made of stardust, and Peach ended up in the Mushroom Kingdom thanks to Rosalina sending her through a warp pipe to avoid a threat.
Previously, Peach and Rosalina's relationship was never elaborated on in the games despite a healthy amount of fan speculation, so the movie making this canon wasn't entirely unexpected.
Mario series creator Shigeru Miyamoto was asked about this change to the canon by Nintendo Dream (via machine translation). Miyamoto explains that he hadn't decided on Peach's background, and that his approach was to not be bound by having to stick to story beats established in earlier entries (which is why there were no Nintendo movies for a long time). However, when it comes to Peach's new lore, he says he'd like to stick to it as much as possible for future entries in the Mario series.
Granted, as someone who has played every mainline Mario game and probably cares about the lore more than most, I can't imagine this ever actually coming up in a game; at least not in a way that's significant. Mario games have always prioritized gameplay over pure storytelling, and while there are nuggets of info for people to dig into (Rosalina's Storybook in Mario Galaxy for example), it's never a priority.
