I like that in a universe where most of the sentient races just happen to be Bipeds with fingers and voiceboxes, somehow the fact that they might share eyebrows is what strains disbelief.
It wouldn't have bothered me one bit if everyone started off with eyebrows. I don't like retcons. I've already suspended my disbelief for the established species lore. Needless retcons needlessly wreck verisimilitude.
We can add previously undiscovered history to existing species. We can add entirely new species. Adding eyebrows, though?
As I asked before, why not give them to all of the alien species? We could even remove them from humans. By your logic, it shouldn't upset anyone, seeing as it's such a minor detail.
In truth, it's a jarring change to the face of an iconic species in a game based upon face-to-face contact. It's also a bizarre logical departure from established lore.
As I said, I think it was a simple oversight that won't stand, and I'm not the least bit worried this will appear in-game. I'm just dropping in to offer some viewpoints. It seemed like the thread was leaning heavily in the "Yay eyebrows!" direction, and I couldn't have that without offering a few words of dissent.