In my opinion, the idea of a cv taking place in the future a century or so after Soma is nice. Here are my thoughts:
through the years following DoS, Julius continues to fight evil but eventually dies of old age (he has no heirs). Yoko settles down and has a family and Alucard is just the same keeping a watch protecting humanity. Soma and Mina do get married, grow old, and eventually die of old age. In the year 23XX, a man/woman loses everything due to no fault of their own. Despite being devoutly religious, this individual suffers tremendous misfortune to the point in which he/she is dying from a curable disease because he/she has no insurance and thus can't afford the treatment. At the time of his/her death, they curse God and all other things and in that moment of immeasurable rage, swears that he/she won't except dying and vows to spend eternity spreading pain, misfortune and suffers among humanity. If he/she had to suffer through life, so should all humanity. This rage, hatred and thirst for revenge turns this individual into a vampire and summons the castle which seems to call to this person who follow the call end becomes the castle's new master.
Thus, a new dark lord ascends to the throne. As for the heroes, the would consist primerily of Alucard and Yoko's descendants. There could be other heroes too. As for the castle, it would retain its medieval appearance we're all accustom to. There would be some modern weapons, but wouldn't be as useful as classic magical ones.