My main point is that it does not contribute anything meaningful, or in my opinion can even be counterproductive, to explicitly express "brown colored, female thumbs up" instead of a more neutral "thumbs up".
I see your point that there are some emojis where might be too stereotyped even in the blob form and that there are already many preconceptions about how some blobs are understood. The police officer blob or the flight attendant blob are good examples. That yellow skin is considered a default for white or that people automatically see a blob with a police hat as male is a difficult subject and I'm unsure how to solve this perfectly in a general way.
It is in no way perfect, yes, but I argue that it's a better direction than going the other way by introducing more and more ways to individualise them.
[0]: http://blog.emojipedia.org/android-7-1-emoji-changelog/#whyg... [1]: http://blog.emojipedia.org/content/images/2016/10/android-7-...