I noticed a while back an app installer for another hosting panel. The installer is open source and very, very simular to Fantastico.
The website doesn't exist and the original author didn't want to continue because of internal probs with other developers, as far as I remeber.
Any way the code is still at SF.NET
I think this would be nice to integret. I don't have any dev time right now, but I would offer a place to host the development of such a project if anyone wants to help to get it to work with ISPCofig.
the SF.NET link is ==> http://sourceforge.net/projects/zantastico/