Isn't it slower querying elements via attributes? Whenever I find a «brand» new way to work with CSS (or whatever they wanted to call it), I'm skeptical. Most of the times they just redo what IDs and classes were made for, but way worse. While this might have good intentions in mind, it's just adding classes via attributes. Also it's explained very badly, I had to click three buttons in order to get examples.
Agree with the rest of the stuff you've said though. I just don't see a place for this library.