I had thought that was the default behavior of the system.
There is an option for auto notification under Setup -> Tickets -> Options ->
Auto-Reply to Client Never Ticket Creation Only All Client Updates
I think that would be a brilliant feature.
Sometimes the workload is to high that a quick response / solution is not possible. All tickets that are not assigned to a technician or were not updated lets say within two days, get an email to say: that we are aware of the issue and sorry about the delay we will do our best to get back to the user as soon as possible. This is a bit like waiting in a phone queue.
It has its advantages and disadvantages. The advantage is not manually to go through the open tickets and to ensure that the user is kept informed. The disadvantage is that it has to be carefully setup to ensure to make sense to the user and not to many emails are nu-necessarily send.