Can you explain more about how your course works? How long is it? etc
I have a few thoughts about this ...
Firstly, I personally don't think it's a good idea to hide "old" parts of the course - it's important for revision purposes to be able to see what has been done and to be able to access old journals, old forums etc
Secondly, there's the "zoom" feature that lets you/students show only particular weeks to reduce load time ...
Thirdly, there's this idea to allow teachers to selectively hide whole sections (weeks/topics) ... A public/draft feature to hide/show topics
For what it's worth, I can sympathize with this problem of courses being long. Some undergrad classes I teach meet three times a week. Over thirteen weeks, with 39 entries, that get's a big long when studetns have to scroll down that lengthy list to get to the relevant class near the end of the semester.
Personally, as the admin I'd just like to be able to higlight the relevant course week and that Moodle start the class list with the one I've highlighted (i.e. put class 15 at the top of the list if that's relevant, then at class 39 start with class 1-14). Of course, I also really want a general course content area at the top--and I have to use week/topic #1 for that right now--so before implementing that idea it would be important to add that 'overall course' section option for the top (which I know is already in the suggestion database).
There's several ways to go and I think this needs some more thought before any implementation, so I've started a new topic over in the Course Formats forum to talk about it.