If they do some sort of universe/mythos-broadening move to allow room for more powerful antagonists, I'm cool with just enough Sparda talk to properly contextualize the conflict between him and Mundus within whatever the larger order of things is. It just needs to come along with making it clear that the power of Sparda is no longer some sort of trump card.
Yeah, in the end, the only way the story will be able to move forward in a poignant fashion is if Dante is actually challenged again by new opposition that "Makes Mundus and Sparda's battle look like Tiddlywinks".
And ideally, at least some big bad/rivals that outlive their initial game appearances, so that we have a believable upping of the ante when Dante and friends can't wrap up everything nicely by the end of DMC5.