I don't know, I thought the DMC series was fine. One theme in DMC was that not all demons are evil, and to add angels to that isn't really necessary. I suppose they could do a 'not all angels are good' thing, but we already got that from Mundus and some other demons that were considered 'angels'. Actually, Mundus himself is supposed to symbolize God (only evil). So angels already exist in DMC really, and I don't know what they can do with them story-wise.
Though I guess they could do a story in which you find out that the demons that look like angels aren't actually angels. Maybe angels are more like cherubim or something, pretty terrifying and on fire. But maybe those 'real angels' would be good guys, and maybe Kyrie could be turned into one. That way Kyrie would find some use as a character, and she would also identify more with Nero because now she knows what it's like to turn into a different being.