When I was first introduced to Callisto, I understood it to be an effort to release several Eclipse projects simultaneously. This is still my understanding, but it seems that Callisto has evolved to mean a lot more to many folks. Some talk of Callisto in terms of a universal installer with a consolidated update site. In fact, there is some work going on to provide the consolidated update site, but an installer of any form was never part of the original plan. I'm pretty sure that it's still not part of any plan. While I agree that having a super deluxe GL-6000 installer would be cool, it's just not part of the original promise of Callisto.
What Callisto is is still pretty important. In the past, there has always been latency between the release of the platform and the release of other projects So, for example, if you wanted to use the latest and greatest version of the platform with--say--WebTools you might be out of luck for a few months while the WebTools team worked to their own schedule. With Callisto, you will be able to use the latest version of the platform with the latest version of WebTools on the same day. Or at least within a few days. Heck, in my mind even being able to use the latest and greatest of everything within a few weeks is still pretty good.