The key design difference seems to be to use a runtime script and data/x attributes to allow customisation and perform style pruning, rather than using config files and build scripts. There are clear downsides to this (as well as upsides, such as faster ramp-up time), but they're not really being presented honestly.

From my perspective, it's hard to imagine someone adopting this as core tech for _websites_, because requiring a blocking script before any styles can load is an absolute deal-breaker for me. But perhaps people will find some utility from it for prototypes, and in environments (perhaps electron apps) which are less sensitive to blocking scripts.