I could see it as some kind of test by the Force Edge...honestly, that would have been fitting for Dante to prove himself it's new master when the Sparda fully awakened in DMC1, but since you had just fought Nero Angelo, one Boss Fight right after THAT epic showdown would have been kind'a anti-climactic. Some kind of inner battle like Sparda as a representation of the Demonic power within the twins or even Nero if Capcom revied the Classic story and decided to run with the hints in DMC4 that suggest Nero IS Sparda reborn in...would be fitting there.