Wasn't Getsu Fuuma Den a futuristic Castlevania?
This is actually a marvel villain named Whiplash, but it's not a bad idea for what a future Belmont could look like.
(https://i.imgur.com/Lre8q04.png)
Vampire Hunter D?
Ignoring the obvious fact that is an Alternate UniverseNow that you mention it, LoS did have a fair amount of sci fi to it. I liked that they went with this sort of demonic sci-fi route, bio engineered virus that turned people into demons and shit, though it's just too bad that it was all sort of half baked.and in my opinion they kinda took the spotlight from the magic and fantasy elements, something important in a Castlevania title to me.(click to show/hide)
I personally like the Sci-Fi elements, but restricted to sections like Frankenstein's laboratories, in the same way Clock Punk is usually rectricted to the Castle's Clocktower, allowing the game to have more variety.
Vampire Hunter D?
Wrote about this way back, but was with spaceships instead (http://castlevaniadungeon.net/forums/index.php?topic=7539.msg168467#msg168467). It was a cringe moment in my life that I'm not really ashamed of :P
(https://castlevaniadungeon.net/forums/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FnTSaQDN.png&hash=50b94e4cf1316d01004e05d10413a64d63919bb9)
I think this is F**** Cool