[fastball]

Doesn't @emotion's babel plugin already do this, or am I missing something?

[lf-non]

Not quite. Emotion doesn't do the atomic splitting - ie. one class name per style rule. This splitting results in ugly looking HTML but if two components are using some common subset of CSS rules they will partially reuse the same css classes.

It is closer to https://www.styletron.org/ in that regard.