It was more of a valid theory when it was possible Ripley 8, with her genetic memory stuff, could still have been featuring. Hicks would make sense to feature as a hallucination along those lines. He'd be the one figure she'd associate with who'd be seen as a fellow fighter, in all regards.
Of course, we don't yet know that this Ripley isn't another of the clones, but those other recent quotes make that unlikely.
Still, he could just be featuring as part of a dream sequence. Have to wait and see.