Well one thing i know about vergil is that he hates humans or half breeds. Is bad enough to think that vergil, nelo angelo or whatever, is in the DB than to suggest that someday he will overpower nero who is human and become the driving force within him which i see as highly unlikely. If and only if vergil is the DB, then i believe after consuming enough power to substain himself he would break free from neros arm making the DB the thing of the past and vergil been reborn. Although i m certain he would not return as a human, afterall is what he wanted to give up his humanity to attain power. So lets say Dmc5 will be all about vergil trying to rediscover himself because due to memory lose (after all as nelo angelo he had a hard time remembering who he was and what reason he was fighting for) and settling the score once and for all with mundus and maybe dante could back him up or something. As for nero, he could go back been a lover boy or something like that....u all dig...