Another interesting question is whether those other namegivers (Obsidiman, Windling and Tskrang) are part of metahumanity or not. We know Elves, Dwarfs, Orcs, Trolls and Humans are highly related and basically different expressions of the same species, but can humans also turn into Obsidimen, Windlings and Tskrang? I strongly doubt it. Obsidimen in particular seem like something completely different, being part of a life rock and all that, but I've also come across a hint that someone in the Shadowrun universe (a CEO I believe) goblinised into an Obsidiman.
Speaking of the others being expressions of the same species, that would actually mean that trinomial nomenclature would be incorrect. Why do I call them expressions of the same species? From what I understand, metahumans are almost completely interfertile with each other, but you never get a half-orc, half-elf or half-troll. You're it or you're not. It's more like eye colour that's either blue or brown, and two people with brown eyes can have blue-eyes kids. Except that growing into a troll is vastly more complicated than the pigmentation of your eyes, but I don't think you can technically consider them a separate species or even sub-species. It really comes across as if the difference is merely the expression of one or two genes. And magic, of course.