Street Fighter V's F.A.N.G. concept was actually based on a character planned for a cancelled Darkstalkers



"The secret of secrets is that F.A.N.G’s concept was actually of a character named "XXsuXXXX"¹ in the aborted NEW VAMPIRE"
Translated from the image above.

Most have assumed a new Darkstalkers was in development at some point and this appears to be confirmation of such from Takayuki Nakayama.