Have you guys (developers) thought of a intelligent update system for ISPC? Something to simplify the update process. Where the admin can login to CP and click on a option to "Check for updates", if a update or newer version of ISPC if found, then it will download the update/patch and patch/update ISPC and HUP ISPC. You can secure the update process by implimenting the same SSL certificate functionality that Rehhat uses to authenticate packages are genuine after downloading.
I think for Debian a deb package is interesting but make more works for developers when must support Package systems for Deb, rpm and more .
since some parts of the setup need the root, I'm not sure if it's even possible to do it with an online update system with an apache user
The ISPConfig daemon, yes. But not the interface. And allowing the interface to execute scripts with root permissions or pass scripts to the daemon is a security risk as planet_fox pointed out. A online update function will have to be implemented very carefully. But my main concern is who is willing to build and test all the additional update packages for these partial updates as this can be a fulltime job for all supported distributions and will double the time for testing new releases.