I also found this thread very interesting, and then I got here and thought I recognized your username. Turns out you asked to try the alpha of my own tool Cicerone (
http://cicerone.co). Hi!
Cicerone doesn't yet do the kind of thing discussed here because it is originally designed to be a rich structured content editor with customizable HTML/CSS components, as opposed to a design tool. However the more I use it myself, the more I find that designing anything in CSS is the biggest PIA, and it would be really cool if I could bring a little sanity there. So I've been thinking a lot about how to do this. Stay tuned (but don't hold you breath, it'll be a while.)
PS: and if you do get around to poking around with Cicerone, do let me know your thoughts: good, bad, or random, I'm happy to nerd out on tools. Cheers Stephen.