"Empire" generally implies "imperialism" which generally implies a racial hierarchy. Or at least that's one argument.
I woulda liked "four nostrils, but otherwise the TNG design" to become the standard.
Oh, what if it's a World War 3-era combat drug, like the stuff Q alludes to soldiers being addicted to in Encounter at Farpoint?
Also there had better be a good explanation in future episodes as to why the hell Dr. M’benga keeps a couple of vials of punching serum handy at all times.
He was a frontline doctor during a conflict with an enemy that considers medics viable targets.
Structural differences in their larynx, tongue, or lips seem likely.
I must say I'm already a big fan of Pelia.
As always, I feel compelled to point out that Turkana IV was never said to have been a member of the Federation - they “severed relations” with the Federation, but that doesn’t necessarily mean they were a member (in fact, I think it strongly suggests that they were not, as that’s a very clunky way to refer to secession).
That's a reasonable objection to raise but I'd counter with the point that it seems unlikely that a human colony could be established except under the auspices of the Federation, or at least United Earth.
We provably aren't seeing that, as there are characters (Kor, L'rell) who have appeared in more than one variant of the Klingon makeup. The implication is obviously that these are different interpretations of a single species' appearance.