And I'm featuring in it too :lol:
Personally, when a series gets to this stage it's usually a money-spinner and not much else. It's rare for a company to pull its' socks up and make something awesome fifth time around, if it even gets that far at all in the first place.
To me, DMC4 was testing the water with the introduction of Nero and the whole "looky! it's on xbox360!" thing. It wouldn't surprise me if the series did one of two things:
1) Completely ignore the Nero thing - like, not even mention it and treat it like a spin-off rather than part of the series, before making a game that revolves around the usual suspects once again - with maybe a hint of Vergil just to pretend like they're going somewhere with it, even though they probably won't.
2) Focus solely on developing Nero's story, whatever the hell that is, with very little concerning the other DMC stalwarts except as cameos to appease the older fanbase.
There is a third alternative: Nintendo get a hold of the franchise and turn it into a Wii game that's fun for all the family.
Could happen...