We only consider creating new fora if there is a demonstrated need that a new forum is necessary.
We would look at the amount of threads, posts and views regarding certain themes or subject areas as well as requests such as yours.
To date, yours has been the first request for a forum devoted to the Vinaya and this thread is one of only a handful of threads on the subject of the Vinaya since our inception at the end of 2008.
Until there is a groundswell of interest in the form of actual threads on the subject of the Vinaya and a lot of activity on those threads, then I am disinclined to create a new forum specifically for the Vinaya.
You are welcome to create threads on the Vinaya at Dhamma Wheel - the General Theravada forum might be a good place to post your thread.