Perhaps to keep our forums more active, we can have a requirement that members who wish to use the chatbox must make atleast 50 posts every month.
For example, in January I have 10 posts. If I want to be able to go on the chatbox in February, I need to get 40 more posts. I get my 50 posts and then it's February. The chatbox is still unlocked.
If I want to be able to go on in March, I must make 50 more posts. When it's March, I only have 45 posts. The chatbox will be invisible to me until I get 5 more posts. Then, I collect posts for April.
It's kind of complicated, so I'm not sure if you'd be able to do this.