My only issue is I can't and don't want a watered down PG-13 Blade.
I think that connection is fantastic.
As far as the Netflix route, what if other folks who used Nightshade had an effect that turned them into vampires? You could backtrack and tie it in that way. Maybe nightshade was around for hundreds of years and some got turned after the continued use wrecked their bodies and they used human blood for staying alive.
Just a thought.
You want to change the entire history behind vampires?
Nah, that's actually a dope idea, we're on the same page.
Better yet breh, how about Dormammu puts out a call to all the dark supernatural creatures since he's bound by the pact he made with Strange against direct interference?
This undercuts the history and mystique of vampires and other supernatural creatures,as well as for Blade to be Blade he would already have had to been fighting those creatures for a long time and be a expert. I don't like the idea of on the job training Blade.