Letts re think about this.
I was actually considering getting Mario and Luigi Super Star Saga remake for the 3DS, and while thinking about I came across the news that Nintendo registered a new trademark for the series in January. Could this rumor be slightly off and SE is actually behind a new Mario and Luigi game? Would be less exciting but it would not make sense for Nintendo to have Mario RPG and Mario & Lugi.. kinda redundant.
Maybe they will kind of merge some parts of both? Nintendo has gotten real strict with not creating new characters in Paper Mario, and of that's the case going forward with M&L (which introduced a lot of non Mushroom Kingdom characters) then a reboot of the franchise lead by Square Enix and made in isometric camera could be what's happening. Take a little of both series, limit it to just Mushroom Kingdom (a decision I'm again) and there ya go.
Just speculation on my part.