Yes, at Nintendo's digital event yesterday they announced a brand-new Mario & Luigi game for the 3DS, and its one of the most unusual combinations... A [Paper Mario and Mario & Luigi] game, mixing both worlds. Honestly the concept of combining the two is quite intriguing, however there is one big negative, it's Paper Mario + Mario & Luigi, but no Paper Luigi, you don't get to play as the paper version of Luigi as well as Mario, Just Paper Mario and the two normal Mario and Luigi
Although it may have been that there were programming limitations, they were able to bring in the other characters and make them a part of the tale the game tells, they share a scene where Bowser meets Paper Bowser and Paper Peach meets Princess Peach.
In my personal opinion, I prefer the style of the Mario & Luigi RPG games over the Paper Mario RPG games. The biggest and coolest thing in this game shared so far is the large Papercraft Mario which is made like the ones you can print up and fold into boxed characters, but is gigantic and can crush your foes by rolling over them. Hopefully this feature is expanded upon and used a bunch throughout the game, and hopefully Paper Mario doesn't blow away when Mario & Luigi steal the show. But all-in all the Papercraft Mario looks awesomtacular, Game on and Keep it Rehl!
Source: Paper Jam E3 2015 Site