Service subscribers can be used by services knowing exactly what services they need (requires a static list of identifiers), creating service locators from a compiler pass remain the only way to collect and map services corresponding to a given tag, injecting the locator by hand into the requesting service.

Would it be interesting to give the ability to service subscribers to request all registered services for a tag (tagged services subscribers)? This could be done by introducing a variant of ServiceSubscriberInterface like:

interface TagSubscriberInterface
{
    public function getSubscribedTag()
    {
        return [
            'console.command', // request access to services tagged "console.command"
            'console.command' => Command::class // skips non Command subclasses
        ];
    }
}

It would remove the need for creating compiler passes that are dedicated to collect services without performing any special treatment on those.