This is something that I've suggested on several occasions. In fact I suggested that very new members should be restricted in posting in some threads as well.
Then how can they rank up if they cant even post on an existing thread. I thought limiting the creation of threads for newbies will be a good idea but not even for replying.
As for them to focus on reading and understanding how this forum really works this would be a great rule for them because as we all know, there are no other new things to be discussed here for the reason it has all been created and all they'll just have to do is to search for it.