Etymology should stand alone because it crosses, permeates, and pervades any one language (family), and can't be confined to individual SE language websites.
A helpful analogy is Reddit's /r/etymology.
Etymology is already on topic on our English Language & Usage site. We have many language-based sites where etymology is on topic for each respective language. We prefer not to create a catch-all etymology site without assuring we have an audience on board to support that language. The proposal was eventually removed automatically due to our minimum activity requirements.