This definitely sounds like it could be a good way to get new users involved, and it could help close that initial gap of turning a registered member into an active participant.
One manual way to do this today would be to create your new introduction topic every week/month and then edit the automated welcome message to link to the current topic.
This also sounds mildly similar to a plugin we’ve been talking about internally that would pair two users together to encourage more collaboration and pair programming amongst our own team. This could be additional functionality (or a fork) of that concept — where instead of choosing two users at random, you could automate a topic that “pairs” a larger group of users together who meet a certain criteria (e.g., signed up within X time).