When satisfying dependencies, portage should check try to minimize the number of packages pulled in to satisfy a combination of atoms such as >=dev-python/python-2.5 and <=dev-lang/python-3.0, where both atoms can clearly be satisfied without pulling in python-3.x.
This is fixed in svn r4315. With this behavior, maybe we don't need a syntax extension as suggested in bug 4315.
(In reply to comment #1) > This is fixed in svn r4315. I mean r14432.
This is fixed in 2.2_rc42.
This is fixed in 2.1.7.