When using Apache there is a 508 error displayed. I don't know how this is achieved and have asked CloudLinux to confirm.
The main problem here is that with a 503 error, that currently happens when a user uses too much CPU or too many entry processes, lsws restarts automaticaly. We need to prevent this from happening. It would also be nice to be able to customise the 508 error page like you can do on Apache to give the user some more details about the problem.