Hi Hazz, your idea is well received. We have wanted to do this for a while, discord is implementing these features in future updates so we are waiting for the necessary permission set to able to achieve what you are requesting.
Right now I do not know of any viable way to create private rooms in discord, the only way I believe is possible right now is by admins creating pre made named rooms and adding user limits to the rooms, this doesn't really make them private and would see a host of unused rooms be made to support this.
If you know of a better way, please let me know. May I also ask in your opinion why you want private rooms and how you will think they will be utilized?