There's already an "initial-install-p" flag in the .info file which causes packages to be mounted during installation, using the package key as the mount point.
What exactly do you want the new feature to do that's different? Naming the mount point would be useful (perhaps a "default-mount-point" tag?). Better than mounting during installation would be to auto-mount when any package requiring the utility package is installed and enabled.
BTW I've just tracked down a bug in the code that autoinstalls packages during OpenACS 4 installation. The package instantiation callback routine apparently isn't honored. This is why you have to visit the "groups" admin page in acs-substite to get the main site's membership group created. There's a hack on that page to configure the subsite if it's not been configured - which should be impossible because the callback does the configuration.
Oops.
I'm going to look into fixing this bug and will then post some information about a big can of worms I've opened by inspecting this code and the old aD 4.1.1->4.2 upgrade packages found in sql/[postgresql | oracle]/upgrade. For a good time take a look yourself :)
