How often does it happen you have to open a new subforum? Once a month? Once a week? Once a day? Every hour?
Moderators and Admins should form a team, so if the moderator sees the need for opening a new sub(subsub)forum he can ask the admins to do

In our forum, there are currently 5 users who are able to create new forums, but no one of us will do it without a team-discussion (including all the moderators).
And, in you have a lot of subforums, really nobody will find the right place to put his content (kiss - keep it small and simple

)
zenit10 wrote:person who i dont know.
In my eyes the biggest problem is that you as the board owner give control of main parts of your forum to persons you don't know. As an owner, in most countries of the world, you are responsible for all content at your board. So giving control to unknown people is like stepping with one foot in prison

For sure, you can write a mod that allows your moderators to open subforums in their "moderator-responsible" forums, but i don't thing it will find the way into the core code, so
mod-request-area in phpBB will be the right place for your suggestion
