This is a great idea.. However, what about the "non ruling" parties. Wont the get a bit complacent. Also, this might bring up rivalries.. and promote groupism.. I feel every now and then the parties must be shuffled. Also criticism must be taken in the right spirit.
As long as things are kept "just for fun" all will be well. If things get personal, it could be the downfall of the forum.
Cheers.