I don't think the functionality's gone, you just have to get to the right place. The new, simple UI won't let you do it.
The service/application split's simplistic, as we've discussed before. We really need three categories - true service packages that aren't meant to be mounted, mount-once packages that provide a service + UI for other packages (general comments), and general application packages meant to be mountable under a variety of subsites.
The second category should always automount under the main subsite IMO ... the right thing to do, probably, is to add the auto-mount callbacks.
