I would be okay with a DMC5 continuing from the DMC4 story-but as others have said, giving Dante more of the spotlight, or at the very least, equal footing, with different enemies/levels. Or hell, even having the ability to choose between Nero or Dante for all missions-playing through with both unlocking specific achievements, costumes, etc.
I'd also be okay with them continuing on from DMC2 (which I still haven't finished...in all fairness, gaming hasn't been top priority lately, which is why). Whether Nero makes an appearance or not, I'd be okay with it, though a little sad if not. I figure a game incorporating all of the major characters would be a good way to go-because if such a game were created, I imagine it would be the last one of that particular era. Not sure if Trish, Lady, or Lucia would be playable or not, but if they're in the storyline, it would be nice to see them in all of their ass-kicking glory.