But what Eliezer is describing is not a "new, hitherto undescribed emotion", it's really just a chronic, low-intensity activation of well-known emotional states like shame and embarrassment. Many people nowadays believe that 'microaggressions' exist and are a fairly big factor in folks' self-esteem and even their ordinary functioning. But that too used to be a "new, undescribed phenomenon"! So why would we want to reject what Eliezer calls "status regulation" which is even less radical, being just a minor twist on what was previously known?
In the Facebook post that sparked this, Mysterious Emotion X is clearly described in terms of other-regulation: a "status slapdown emotion". Shame and embarrassment, chronic and low-grade or otherwise, are directed at self-regulation, so they aren't a good fit. Envy (and "a sense that someone else has something that I deserve more", which sounds to me like resentment) is specifically excluded, so it's not that either.
I'm pretty skeptical of the microaggression model too, but this isn't the place to be talking about that, if there exists such a place.
Todays xkcd
I guess there'll be a fair bit of traffic coming from people looking it up?