If anyone wants to RP their site characters in the Free Roleplay section they are able to do so, even before approval. The only thing they are unable to do is RP in the main forum to prevent people from gaining Poke from an unapproved character.
Also. There is Character Discussion board on the forum already for if people wish to discuss what they want to happen in their RPs. And even for RPs in the Free Roleplay section, you can always discuss them via the Chatbox, or PMs. Or, as me and Ripple are currently doing on our Unova RP thread, use titanpad.com to keep track of any RP ideas and character stuff. ^^
I personally find titanpad more useful than another board for threads as you can then keep your ideas to yourself so that it is more of a surprise to whoever is reading etc. Also, you can link the titanpad to whoever is in your RP, and not risk other people intruding etc.
I do appreciate your idea, but I do think it would be rather unnecessary as there are already other options. X3