Eg.

#[Handler(Some::class)]
#[Handler(Other::class)]
#[Route('sync')]

As replacements/alternatives for

        'routing' => [
            'App\Message\SmsNotification' => 'sync',
        ],

and MessageHandlerInterface 🤪

Perhaps it's considerable to expose some tools in a contract package, for other bus implementors to leverage. But Messenger component will do i guess. We could even think of a interop messge bus contract.