Backup MX Service on cPanel DNS only.
At the moment I have a backup mx box on my second name server, this holds mail if the main box goes down. However dns only has exim already installed, it just does not utilise and option for hold backup mail for all domains synced with it.
It would be good to provide a backup mx service in the cPanel DNS only install as this gives you mail redundancy as part of the cPanel product.
It should be a fairly minor change, as I would imagine the dns server already has the domains listed in a MySQL Database where it can be gererated and added to the relevant file in Exim.