In my perspective, there should be two things on this list:

* Invitations to test new features. "Testing" in this case is
something that can be done by somebody who is an end user who has an
"early adopter" character and who is curious about technologies, but
who is not necessarily a developer. The new feature must be set up
online somewhere: in labs, as an opt-in feature in an existing
Wikipedia or Wikisource, in translatewiki.net or some other site. It
usually shouldn't be needed to install software on your own computer
to test features announced here - installing MediaWiki is too hard for
non-developer users. Announcement of Visual Editor features
deployments in Meta is a good example of this.

* Announcements about new features that break existing gadgets,
templates, features or content in existing projects, and require
change in their code. The change is not necessarily something that the
ambassador can do himself or understand completely, because the
ambassador is not necessarily a coder, but it must be something that
the ambassador must be able to convey to the techie types in his
community. The announcement of the $.browser deprecation by Krinkle a
few days ago is a good example of this.

I would add announcements about new features which are available or can be requested (e.g. "from today wikis can request ArticleFeedback to be turned on").

I would prefer not to have discussions here (with the exception of meta-discussions about the list itself, like this one); there are several channels for that already, and keeping the list low-traffic, high-relevance is much more valuable. On the other hand, pointers to discussions in other places (about how upcoming features should work, for example) would be useful.