Most, if not all RPG's rely on an invigorating and compelling narrative with reasonably in-depth characters to immerse the player into wanting to experience the game. It's what provokes them to move forward with the story, level up the characters, explore the world, etc.
Doing something like that with Devil May Cry would essentially rely on removing every single element of DMC's nonsenical, anime-esque plot to make the experience even last half an hour. Characters would need to be developed seriously, the plot would have to do away with the series' staple style-over-substance cheese, and Dante's god-tier powers would need to be disposed to even allow the concept of leveling up to prove useful, logical, and applicable to him at all. In essence, making a Devil May Cry RPG would require stripping away literally everything that would make it recognizable as Devil May Cry.
Now, a Devil May Cry spin-off game with RPG elements, in the style of games like Monster Hunter or the Musou games might work...but a full-blown RPG? That would be a laughably unorthodox game that I hope Capcom is smart enough to never even attempt.