You can try the <progress> element with a preview build here:
Note that you might have rendering weirdness on MacOS X and Windows.
Build with working implementation for <progress> (only horizontal progress bars) can be found here:
All patches except the support of vertical progress bars are ready to be landed. Should I proceed and (maybe) ship without vertical progress bars support or should I wait for that?
I do not believe it really matters given that Opera do not support vertical progress bars (last I've check) and Webkit did support it but do not seem to support it anymore (mentions have been removed from the doc and I can't have it working anymore).
Actually, even if we want to have vertical support, I would prefer to land what we have and disable it if needed.
I'm not sure what's the procedure here. Do I have to ask for a green light?
If other browsers are shipping without it, it sounds perfectly reasonable to do the same. It won't worsen the fact that authors have to consider that authors will have to consider what happens on browsers that support <progress> but don't support the vertical orientation.
IIRC, new features should use a tracking flag.