I would really like `rm` to just deprioritize the space taken by the file, so if enough time passes and space is needed, old deleted files are reclaimed.

That is, institutionalize the idea of "undelete" -- but still allow `rm` to make a good trade-off between space reclamation and irreversibility.

Manual memory management is still useful for some things, but it seems you're implying GC is wrong in every situation? I'd say the vast majority of software today is better served by GC'd languages (That does not include many forms of systems programming, however).