I for one am glad that Fox still have Ridley on board for the franchise, I mean, why wouldn't they -- Covenant wasn't a critical failure, and I pretty much only read the top critics on RT (74%). Regardless of anyone's feelings regarding the last two entries there's no denying that Fassbender has added some much needed class to the series, and frankly all the appeals to mystery seem mostly emotionally motivated and ignore the crux of Giger's aesthetic; which wasn't so much predicated on mystery as much as the erotic and grotesque transfiguration of sex, death and technology combined. Stumbling on an alien parasite already preadapted to infect a human host is also just not possible without a history of co-evolution anyway; pathogenesis requires an established intimacy, heck the facehugger KNOWS to provide the host oxygen, and it had to have recognised specific human proteins, cells, etc, in order to thwart the immune system's defences and use the host as an incubator. I don't know what would motivate some elephantine Old Ones to create such a messy, penile creature -- it's so evocative of human sex organs, after all -- but I do know what would motivate a sexually impotent, emotionally paradoxical and mad android. Love it or loathe it, it's logical.