Doing so would support code editors like VSCodium, because this editor's product.json file is set up to use open-vsx.org as extension gallery.
Hence, if extension maintainers don't publish to Open VSX Registry, users may face some problems:
- Unable to find and download the extension, directly from the editor;
- Unable to have Settings Sync download and install the extension;
- Being forced to manually download and install the extension.
The publishing process is documented in the Open VSX Wiki.