Well, I think that is already available with the host-specific configurations.
I just don't know if:
a) People know about it. :) b) It's too much hassle to setup.
Maybe our installer should create one of those instead of writing the usual to make it more obvious.
It's not as easy when you have a few CNAMEs pointing to the same roundcube installation. Not only that, we have 15 servers running, and sometimes id like to go to a specific one to debug some issue on a specific server. So before you know it you have like 20 different possible HTTP_HOST options. Id much rather be able to load a main.local.inc.php file.
Issues like these is why i follow git release-0.8 :)
Cor