TSo maybe the market for Mario RPGs that put in platformer elements to appear less RPG like to sell to an audience that doesn't play many RPGs doesn't exist anymore. An audience playing the games I listed above would probably find Mario & Luigi and Paper Mario overly simplistic.
I wouldn't say that since Dream Team still sold 2.6 million copies which is more then Fire Emblem Awakening which sold 2.2 million, and is only beaten by Fates at 2.9 million. Of course keep in mind Nintendo includes every version of Fates in those numbers so someone buying one of the versions of that game and then buying the other 2 as DLC is being considered as 3 games sold. So technically, Dream Team probably has the best standalone numbers of any RPG on the 3DS that wasn't Pokemon of course.
So there's still an audience that like that Mario RPG's, whether they're Mario fans who want a different take on Mario or RPG fans that want different take on the genre, or a combination of both. Now Paper Jam saw a big drop where it barely crawled past the million mark and had no legs. But this is do to a number of factors like coming out less then 2 years after Dream Team which didn't help that Dream Team was such a slog that dragged on 20 hours longer then it had any right too, so there wasn't a demand for a new game that soon. Plus being a crossover with Paper Mario, after Sticker Star poisoned the well of that franchise, while also taking the worst aspects of Sticker Star like the generic enemies, locations and Toads, something that fanbase hated, made an experience that nobody wanted.
Basically, there's still an audience for Paper Mario or Mario & Luigi style RPG's. They just need to be creative again and not invite Miyamoto to give them advice this time. A Paper Mario just returning an RPG with a world of unique NPC, locations and enemies again would be enough to generate excitement for that franchise. Mario & Luigi could be big again, but they really need to find a way to expand the gameplay instead of just rehashing Super Star Saga for the 5th time.