I mean, while we're in fanfiction mode at the moment, what I suggest is just one of the things that I could see "working" for the sake of a genre shift, if Sparda's game and story was meant to be a decidedly different one from his son's. Dante seems to get himself involved in what are basically isolated, much more personal incidents in between his regular jobs. Everything that we do know about Sparda makes it out to be that this guy was waging a war against Mundus and his own kind. It'd play right into the Musou series' usual shtick about "A Warrior Worth 1000" dominating a battlefield, to say the least.
Now, of course, I would desire better for Daddy Sparda and Mama Eva as much as the next DMC fan. But with Capcom being as they are currently? Even if the idea is so ludicrous, and there's so much evidence that says why it couldn't (and shouldn't!) happen, I could imagine the .01% probability that makes such a thing a possibility.