Ah, that's different. Hiding arbitrary topics is already planned, we've talked about that. No problem there - that's coming.
Showing only the current week (automatically, for everyone) is the feature in question here. I can see why it might be attractive to teachers - but I fear that all it does is restrict students from looking ahead or looking back in the course.
The purpose of that page is to act as an outline of the whole course, so that it's always possible to see the
context of the current topic, to prepare for what's coming up, to review what's been done etc. By providing this access you help cater for a wider variety of learning styles.
Imagine you're a student. It's Sunday night and conversation is roaring in the final forum of topic 1, and you've written a big post. The next day you log in to continue the discussion and it's all gone, because now we're on to topic 2. You can't even find the resources you need for that assignment next week. (Of course they are there hidden under the activity menu but I think many students will be confused by the interface changing every week)
I'm worried that if the there is a "button" to turn this on then (novice) teachers will see it and use it, thinking it's a good idea without really thinking about the consequences. Granted, they will also be able to get the same effect with individually toggled topics, but the manual process means you have to be more deliberate about it.
Now I think about it, there might be a case for providing this option as a per-user option. That way everyone can choose to have only the current topic/week show, using a toggle button on the course page somewhere.