Engineers, no. Not in the flesh at least. Save that for something that is more directly connected to Ridley's prequels (Covenant sequel eventually, please and thank you).
The Pathogen, though? I'd be all for seeing it used/integrated in the Alien biology in interesting ways, like what Alex White did with Facehugger impregnation in their novels. I can see the Aliens perhaps secreting it (or something like it) as part of an eggmorphing process, if something like that were to ever be attempted again in a film, for example.