I had a quick look in the tracker and there appears to be nothing open requesting it be put back, so as it's entirely possible to get the code back from previous versions and employ new course format setting functionality then there are two options:
- Create a tracker issue (preferably with the completed code as a patch to the master branch - being an improvement) to have optional "Show only this section" in the core course formats.
- Create a clone of a core format and implement your own contributed course format.
With '1' then you run the risk of doing lots of work and it not being accepted. However, with both cases you would have the code, so if '1' failed then '2' would not.