Although easier to manage, having the same events for Master and Sub requests means that a lot of listeners start with this line of code

if (HttpKernelInterface::MASTER_REQUEST !== $event->getRequestType()) {
    return;
}

If listeners registered for which type of request have to be called we could improve performance and avoid enormous and useless log entries when you have multiple Sub Requests in your application (basically when using the render() function in Twig)

Current events could be left untouched in order to preserve BC but add new events that would only be called in Master or Sub Requests

All comments/opinions are welcome, would like to see if this is feasible before submitting a PR.