I had an idea similar a while back. Mine was a basic merger of all CV1-type games(CV1, Haunted Castle, Chronicles, SCV4) and try to make a definitive "Simon Belmont" Castlevania game that has parts from all the games. Also, pump up the stage count to near CV3 numbers. 21 Stages(including alternate stages you discover by finding different paths, the 21st stage being the Castle Keep, the short walk through the entrance quarters, up the iconic staircase to Dracula's lair), 21 different boss battles(some compose of multiple enemies, like the twin mummies, Frankenstein & Igor and Slogra and Gaibon, or multiple forms, like Dracula).
My idea was that it would start in town(cutscene of the Spring celebration hinted at in the manual), then Dracula's resurrected and sends his hoards to kill the townspeople. First stage, Simon enters as people flee past him and jumps into the fray. Second stage would be the Abandoned Abbey where they resurrected Dracula(in the Chronicles cutscene). Then, you venture via SCV4 route on your way to Castlevania(the actual castle entrance halls being, perhaps, the 5th stage) and the games start to merge closer.