See rough plan here: #23023 (comment)

At the moment, --enable_workspace and --enable_bzlmod are already no-ops on HEAD (and rolling), but the code remains to facilitate backports to 8.x. With repo contents cache PRs cherry-picked, we can now start removing WORKSPACE logic from HEAD. This will remove a great deal of maintenance burden, and allow us to clean up age-old tech debt.

List of user-visible changes:

• The WORKSPACE file will no longer be read or processed. It will remain a repo boundary marker file for backwards compatibility.
• The bazel sync command will be removed. It's replaced by bazel fetch --all.
• Several fields will disappear from the native object in .bzl files loaded for module extensions and repo rules, including native.register_toolchains, native.bind, etc. These never worked, but the fields were there; they'll be removed.
• The flags surrounding the "resolved workspace file" (--experimental_resolved_file_instead_of_workspace, --experimental_repository_resolved_file) are deleted.
• The output of bazel mod show_repo will no longer contain meaningless stack traces.