IGA didn't make a Vampire Hunter D game, they made CV SOTN.
yeah The CV team seemed to love Vampire Hunter D, the whole Curtis Lang thing. the same goes for Simon in Akuma no Chi Chi no Akumu. (maybe its just a coincidence, but still...) And how Alucard went from looking like he did in Densetsu, to My love is a fire D look alike. I would love to see, a sort of mix Of the two Alucards, as I think he does look very much like D... almost too much. But don't get me wrong there is Nothing bad about, taking inspiration from Hideyuki Kikuchi, I Know I have.
Speaking of CV lore, id have like to have seen where the developers of Apocalypse planed to take the story. Like how
Reinhardt Schneider was Heir to the Belmont clan as well the Vampire killer whip, as I had assumed that he was a pure blooded Belmont. As I always thought that his mother was a Belmont and she took her husbands name (as some do) Sort of like how Jotaro is still a pure blooded Jostar, he just had Kujo as his last name. I really liked this Idea for the Belmont's, I mean IGA changed it so that all Pure blooded Belmont's kept the name Belmont and that's fine.
But also all that with Malus and the bad ending, id love to see how that would have gone down. Shame (for me at least ) that we'll most likely never get to see the plans they had for the CV canon.