A continuation of what happened to DMC4 is what I would prefer. Seeing as DMC2 feels more like an ending, the same way the first Legend of Zelda games are the last ones in one of the storylines of LoZ.
I for one, really do not need any explanations for the story. I've got my mind set on what the story might be. Now what I do want is a Devil May Cry with a combat system that has the best out of every combat system, what made me love DMC4 was its extremely flexible combat.
I would want DMC5 to be very difficult in its higher difficulties, not like DMC4 where DMD felt like a normal mode.
I want epic bosses, like what DMC4 did, more interaction with the bosses and bosses to be more flexible with the combat system so it doesn't end up with just finding a routine. Less restricting bosses, that requires fast action and counterplay, kinda like Dante in DMC4 and to a lesser extent Angelo Credo.
I want the music to be the epic music I've had from previous DMC games.
Lastly, this is more of a wish, but a mode where you can fight bosses from all DMC games, the older ones to be revamped to fit the more flexible system.
Now, for how it would really be, I'd think Darkslayer got perfectly.
