More importantly though, turning the Arcturians into E.T, in any shape or form, is missing the point of their presence in Aliens
to begin with. To an almost offensive extent of misunderstanding the context and the implications.
I don't want Alien to turn into a full blown Mass Effect Space Opera, although I love Mass Effect.
Not necessary. AvP is the space opera? I don't think so. With Engineers it's become the space opera? No. New races can be added, just used on second plan. And the space opera can be without aliens (humanoids) races - like as Dune.
Alien universe is not dead space (with Necromorphs, dead life forms). It's a strange space with biomechanical life forms, there is no border between life and technologies. The strange pilots who grown from the chair, parasites with robotic elements, synthetic androids who was grown like organic life. And this context I never imagine Arcturians as Asari and they all look different and dissimilar each other because they used implants and geno-modes. It's a big a field for imagine. We can even see new alien breed from Arcturians (DNA reflex) - in that case we will see only Arcturian corpses.
I agree mostly, but they state they've never seen anything like the Alien
What you're describing sounds more like varying degrees of transhumanism, which would suit Alien I think, a sectarian organisation of transhumanists perhaps, (E.G Devolver Digital's "OBSERVER_" VG, Starring Rutger Hauer) but not actual living E.T races. The more common you make all those things you've mentioned above, the less other
it becomes and that's a grievous mistake.