[gentoo-dev] emerge optional

I know when you emerge it will read USE= and compile in options if it is in
your USE=.  Is there plans to add the ability to have optional packages?
ex. gentoo xine requires libdvdcss.  What if you don't want it.  Could
future emerge prompt for option libs that aren't installed.  In the above if
it is already installed use it, if not prompt the user.  I could see this
could supplement the USE= for rare libraries or even replace it.

Robert Davis