There are sequels to Prometheus and Blade Runner coming. Sure, they aren't coming anytime soon, but heck if Ridley Scott isn't talking about them anyway.
Prometheus left us on a bit of a cliffhanger. Most of the cast died, a xenomorph-like alien was birthed, and Doctor Elizabeth Shaw was still in search of the Architects with David's head in tow.
So what happens next? According to Ridley Scott in an interview with MTV, you have to more or less pick up where you left off, with David's dilemma of needing a body, and the danger that represents:
You can't have a person go off into the galaxy and have a person who's still got his head off. Once that head goes back on, he's really dangerous, but he's also very seductive, so maybe he'll persuade her to put the head back on.
That's your Prometheus tidbit. As for the Blade Runner sequel, Scott says, "It's written and ready to go." He also said he showed it to Harrison Ford, who supposedly called it "the best thing I've ever read." Now, that's a lot of promoting. The meat of Scott's statement comes not from what the new Blade Runner will be, but what it won't be -- a reinvention.
It's very relevant to what happened in the first one. I'm not just doing a sequel with lots of action to how how [much] farther we can go with the special effects, because you can't really. Blade Runner we kind of landed on a somehow very credible future. It's very difficult to change that because it's been so influential.
That's a huge relief for Blade Runner fans. The world-building of that story was so perfect, it would be insane to tamper with it. Then again, Prometheus is kind of a reinvention of Alien, and in this same interview Scott responds to that film's detractors by saying "#$% you very much." So, we'll just have to wait and see.
In the meantime, here's the interview in its entirety.
(via Comic Book Movie)