This ability to entirely hide weeks/topics from students is important to us. Student's don't like to have topics show up in grey that they can't get at. And hiding weeks is important for example in courses that run over the vaccation period. Showing a large number of greyed out boxes for all the vaccation weeks just clutters the student's screen.
I would thus like to see this as part of Moodle 1.3 and will now put in a feature request on the bug tracker.