Maybe it's the Klingons again. If they can't be bothered to adhere to how Klingons have looked for the last 30 years, why bother to adhere to how they've looked for the last year? I jest.
Seriously, since it appears to have lizard-like scales, my best guess is that it's a re-imagining of the Gorn, that lizard species that Kirk fights in that one episode. Since the writers seem to want to lift everything that they can from TOS (like Mudd and Klingon-to-Human transfiguration), that seems like just the kind of thing that they would do. I think that I might actually welcome it being the Gorn, though, since it'd be a more menacing villain than Mudd and alternate Georgiou, it's a species that we know the Federation encountered around this point in the timeline, it's one that we know almost nothing about and it's one that could really use a re-imagined look. Of course, because I wouldn't mind that, it'll probably end up being re-imagined Cardassians or something else anger-inducing, instead.