Another note: while debating this with myself, I've come up with the notion that Meta might be a slightly better place for it. If we had a tag on meta, heavily regulated by mods and top users, and a list of specific projects we'd announce for, that could work.
That post was written when we had no mods. Now that we do, what interest is there in creating such a tag for announcements? Obviously, it requires defining criteria; that could be done in another meta post and copied to the tag wiki.
Do we want this?