
this is just a theory that I have been thinking about for awhile. it is not supported by much fact.
my theory is that the deacon seen at the end of prometheous becomes the first biomachanical xenomorph. the deacon seems to be out of the picture for now but what if the deacon came in contact with the black goo on lv 223. my thought would be that it would slowly mutate into the biomachanical xenomorph over a long period of time. mabye evn the queen.
this is a really flimy theory but it is just something that I thought of to keep the deacon relevant.
another possibility for the deacon is that it is a chestburster form for the much larger ultramorph.
food ain't that bad! - Parker

I honestly think the Deacon was just RS throwing a bone to those of us who wanted to see an Alien lol!

I don’t think this is such a flimsy theory, and I think there are some big relevant facts related to this that do not appear to get addressed that often.
In Prometheus we see the trilobite attack the engineer and what emerges is the deacon. This seems straight forward enough, but maybe we need to rewind a little.
Where did the trilobite come from? We are shown that Shaw could not create life until she became infected by the goo via proxy. So from a point of no life we have life, and in the form of a trilobite. From an evolutionary standpoint trilobites appeared around 520 million years ago, dinosaurs were around 250 million years ago and presently we have humanoids. If you can see where I am going with this, is that dinosaurs roughly come slap bang in the middle between trilobite and humanoid on the evolutionary timeline.
When I first saw the deacon, my first impression was that it looked like a small dinosaur, with the exception of having a projecting mouth part. I thought that the deacon was an evolutionary statement that RS wanted to make and part of the punchline about the engineers seeding planets. The deacon and the engineers have a distinct gigeresque look to them, which I see as being part of their dna, so when we see the sacrificial engineer at the beginning of Prometheus, I think this was not only the introduction of the goo excellerant, but the goo needed a form of dna blueprint to work from, that being supplied by the sacrificial engineer. RS does say that the scene could have been on another world, and simply shows how they have introduced their technology to the planets ecosystem.
All this leads me to regard the goo as an evolutionary accelerant. We know dinosaurs went extinct, but what would happen if a dinosaur was exposed to the goo, could it evolve into a xenomorph type creature?
Moving on to AC, we do not know how David got the eggs for the facehuggers and what he needed to create a xenomorph. I do believe Shaw provided the key to unlocking this because there may have been something in her dna blueprint needed to accomplish this, just as the goo needs the engineer dna blueprint at the beginning of Prometheus. RS has stated that David creates the xenomorph, but which one? Do we just mean the one we see in AC? I think this opens up some interesting possibilities, in that I believe the engineers did at some point create a xenomorph on the back of their dna, just as David has created one off the back of Shaw’s dna
Given all this on board, if the deacon was exposed to the goo, I do believe that there is a case for it to evolve into something different, which could very well be a form of xenomorph. The thing here is that if something did evolve it would be off the back of both Shaw’s dna and the engineers.

Just as a bit of an add on to all this, I don’t know if you have seen Automata (Antonio Banderas), but there is an interest evolutionary statement made in this with regards to AI. The point here is that when an AI has been allowed to evolve in its own time, it will evolve in a matter of a couple of days when compared to the time taken for what we know as evolution happening over millions of years. So looking at the goo as being an AI evolutionary accelerant, we see that the timescale from when the engineer is impregnated by the trilobite, to when the deacon emerges, supports the idea that AI evolution has taken a trilobite to deacon (dinosaur form) over a matter of hours rather than millions of years.

Interesting idea... we never 100% know what happens if the Black Goo effects a Organism that is the result of the Black Goo, but we do see the Hammerpedes swimming in Black Goo without appearing to change again.
I think the Deacon would just grow to a Larger more Aggressive looking version but it would be interesting to see how this Organism Procreates.
I think the Bio-Mechanical Aspect of the Xenomorph will come from a EVOLUTION of Davids Creation, either at the hands of the Engineers or a Hubris of David, i think we could see David Evolve his Body, or see the introduction of a Female Synthetic that either way would show us a Synthetic Construct (Part Organic/Synthetic) and this leads to the Bio-Mechanical Xenomorph.
R.I.P Sox 01/01/2006 - 11/10/2017