Currently I'm loving Jade/Stylus to implement a fairly static website design, and that's just building it with a simple script (with Live.JS to preview changes).
A quick look at HAML and I fail to see how one is more or less verbose than the other. Of course, since I don't use it I suppose I'm not a valid source of comparison.
But to risk negativity, this sounds a great deal like the no semi-colons in Javascript thing a while back.
By the way - no semi-colons in javascript was a good idea aside from a few major factor - it broke things and it was a hack based on loose syntax handling. If it was built into the language design then it would have been a good thing.
What you propose is trivial to the machine, but not necessarily easier for the human.
By the simple fact that no semi-colons broke things and was a hack contradicts the thought that it was a good idea. Building it into the language might be a good idea but it wasn't to try to go around the language.
Just to save some time, HTML+CSS+JS fuses, poorly:
1) page description / layout
2) appearance
3) interaction / animation
4) forms
5) content
6) metadata / markup
7) typography
8) vector art and raster images
You could probably throw in HTTP stuff, cookies, how much the DOM sucks, and multimedia too.
Sadly, bad as HTML is, there hasn't been anything better.
I would agree with you that over the years people have pushed features into HTML beyond what it was originally intended for, but that's not what's being discussed.
Contrast to Jade where I would just go: p some text
and let the indentation sort out the DOM structure. It's simple, readable, and doesn't overuse a set of keys placed more or less to be used infrequently (the <> brackets). All this translates to more productivity.
CSS is different problems, but it still stems from being overly verbose (too many vendor tags to worry about) and lacking useful functions, interators etc. Basically CSS sans a preprocessor is just slow and clumsy to work in.
Also as a designer I find myself telling potential clients that they don't need a designer and should just go with a template or a logo from 99designs. For the longest time I hated doing this, but I realized that if someone wants to spend from $10 to $500 to do something that I wasn't the right person for the gig!