Gobby development has not stalled. We released 0.4.3 with native Avahi support a few weeks ago. However, it is not planned to add any great new features in favor of the sequel I already announced half a year ago. Unfortunately, it does not make as much progress as one could expect it to do, and especially not as much as I would like it to do. My second semester at university began three weeks ago, so I also don't think I get too much done in the following two to three months, either.
The successor of Gobby is going to be called Infinote. It will offer some (long-requested) features the current Gobby architecture does not support, such as different document types, XMPP-based messaging and showing remote cursors/selections. However, the fundamental change is that I want to provide a kind of framework rather than an editor, and to get people to implement Infinote support into their editors so that ideally you can just continue to use your favorite editor for collaborative work. For this to work, I need to properly document the API and network protocol which is also one of the points Gobby is rather weak in currently.
A propos protocol: More and more collaborative editing efforts pop up lately, like Pisara Editor, AbiCollab (which I should really try out in the near feature...) seems to be mature and a GUADEC session description mentions some gedit/collab (over which I did not find out any further details, though). Then, there are of course ACE and MateEdit which I am already aware of. All of these (including Gobby) use different protocols, and are therefore unable to interoperate with each other. Most seem to agree that XMPP is a good base, but there is still the application-specific stuff on top of it that needs to be compatible. It would be great if there was some project like freedesktop.org to agree on a standard for collaborative (text) editing.
The current Infinote code is available in a public SVN at svn://svn.0x539.de/inifinote for those who want to have a look at it. However, most of the ideas do only exist in my head by now and are not written down somewhere in there.