I am 100% sure there will be a `defaults write ...` command and/or a policy setting via Apple Configurator (mobileconfig profile) to disable it completely. They will probably push hard on the "enabled by default" part. Since they are literally paying millions to Google...
…which probably won’t work for everyone and their grandmother, because most settings in Apple Configurator require you to have a managed device.
If you have a Mac, you can supervise devices locally. macOS itself doesn't really have restrictions on payloads (except for Declarations, which mostly are sent by an MDM server). Both Apple Intelligence and Siri can be blocked by Screen Time anyway; it's basically a user-facing interface to apply the same restrictions.