My idea of Castlevania V would undoubtedly be the 1999 game. I know a lot of people would expect a MetroidVania instead, but Julius should get his own ClassicVania that combines the very best elements of all of the original games.
More characters to play as from Dracula's Curse and Bloodlines like Julius, Yoko, and Alucard, IV's whip swinging and semi directional whipping like Bloodlines and Chronicles, Rondo of Blood's item crashes and multiple routes to take, etc.