It's painful to have to spend hours synchronizing his copies just because a simple edit or adding keywords has modified your files. If I take time to add keywords then all my files have been modified and it will take hours to synchronize copie to USB disk or copies in the Cloud. In addition, using AWS S3 Glacier is impossible. It gives the impression that Adobe doesn't care of the integrity of files and everyone is just having a single copy of his files.
Why to keep keywords only in the catalog, same for edits metadata (because anyway there's no way to read them back for edits without the catalog)? And the XMP option doesn't seem to work properly as it's still writing in JPG or DNG files.
A simple option like "do you want to prevent lightroom do modify your original files?" would be a time and money saver.
That option already exist. Turn off 'Automatically write changes to XMP' in the preferences. This option writes changes to XMP sidecar files for proprietary raw files, but writes changes to XMP in the metadata header of JPG, TIFF and DNG files.