Yes, I thought this approach should work, but why nobody has done it. The only real issue is file collisions, which I test for aggressively. So far, I've only found a few minor cases that I either worked around or reported to the relevant projects (e.g. some projects package the extension with a generic README.md file) instead of an extension-specific one.
One surprising benefit that I hadn't considered when implementing this is that when I add new extensions or update existing ones, users only need to update the affected layers. As a result, update times are minimal.
One surprising benefit that I hadn't considered when implementing this is that when I add new extensions or update existing ones, users only need to update the affected layers. As a result, update times are minimal.