If you have not seen Prometheus, please do not read further. SPOILERS
CRAZY THEORY ONE
The engineer ship that Shaw and David took off in will be the same ship that the crew of the Nostromo discover on LV-426. This will ultimately be revealed in a Prometheus sequel.
CRAZY THEORY TWO
If the above does indeed happen, the black goo canisters that are undoubtedly stockpiled on the ship Shaw and David escaped in, will at some point interact with LV-426’s version of the worms seen on LV-223, giving “birth” to the process that creates the facehugger. You know the rest.