[sAmI]

I am afraid the most possible outcome will be a sudden increase in the number of "low-quality new threads".

So, instead of making it a punishment if a member does not create any new thread in a month, I believe it is better to offer members some extra bonus to encourage them making new threads.

I also like your idea! But that will actually work for a few months, Requirement "forces" people to do it. If there no requirement for even 20 post, I believe only few members of the forum would complete and no one else. What if there somehow a way to avoid low-quality threads? Like 
A word count or something, Like a person have to write "x" number of words. 200-300 maybe? 
I'm not saying this rule should be forced this would be a problem for people who does not speak english like really well. But this would increase the thread count as there are many good posters around here.