[twhb]

Parallel restyling just kicks the can down the road, asking for free perf elsewhere because we still haven't made it fast. What we need is a low-level style interface - .style but for computed, not CSS-integrated, styles - and then to plug into that using CSS where appropriate, or custom JS where appropriate, or even framework JS. Let people control style selection in a real programming language and you've guaranteed that it can now be done in a way that's fast and suitable.

[pcwalton]

I don't necessarily disagree, but I'd like to reassess where we are in terms of performance once Typed CSSOM is widely used. Using Typed CSSOM to adjust the "style" properties of individual elements is awfully close to doing what you describe: the difference is that matching and cascading still happens, but the semantics become much simpler if you're adjusting individual styles, and it's not clear to me that most of the overhead can't just be optimized away at that point.