I was thinking in a feature for the upcoming kuroo, and I wanted to share it as I think it could be good for portage.
The idea is to improve pretend option to do all checks, as many people (like me) uses pretend before emerging (or even, improve ask option too).
For example, I realized of this while I was installing stage3, after installing nvidia-drivers and xorg and layman. I tried to emerge kde (svn version of 4.0) in kde's overlay, and before, I did a pretend in order to unmask apropiate things.
It tried to pull more than 100 packages, and I let it all night running, but when I saw it, it halted due to a check: it was requesting qt4 to be built with qt3 support USE enabled.
I think as when you do a pretend, it already has digraph available, it could also check one by one, the USE dependencies and warn if some are not satisfied.
This way, you ensure emerge won't halt becuase of this trivial things.
This could be applied to kernel config checks, and so on..
What do you think?
*** This bug has been marked as a duplicate of bug 2272 ***