Take a look into the process of become a Member state of the U.N. It's not easy. It doesn't happen often. but it does happen. one of the biggest hurdles to it is, "international recognition as a sovereign state". The same could be applied here... The warlocks need to demonstrate to the other signatories that they are independent of the White Council. That'll be tough to do, until the warlocks wage a successful "rebellion" against the White Council and get the White Council to let them govern themselves.
The thing is, when a new country comes into being it's with international good will. When South Sudan broke away from Sudan you didn't have the US, Russia, China, and various European powers calling Sudan a wimp for letting it happen. You didn't see them circling like sharks on a blood trail, working out how they could occupy and annex both nations.
Many of the other signatories of the Accord are predators. There have been several cases where it's stated "The White Council always presents an united face to the outside" because failing to do so would attract predators. That was a big part of Summer Knight - the rest of the council didn't want a war but they needed an excuse to hand Harry over to avoid creating a precedent setting event. The vampire courts, nickelheads, fomor, etc would love to see the freaks wiped out and if someone gave them a chance to do it they would gladly use any pawns who are available.
As for successful rebellion etc - China has a seat at the UN. In the 50s the Nationalist Chinese government had that seat - even though the Nationalists were reduced to Taiwan while the "rebels" held the rest of China. Eventually the rest of the world recognised that Red China should have that seat because they were the government of the country. If there's a "we won't take this anymore" rebel movement in the White Council I can see the White Council Accords "seat" held by the Merlin - and when he dies whichever faction replaces him getting the seat.
But let's look at this from another angle - what would any other group of mortal spell casters gain from signing the Accords? They are already "protected" from supernatural predators by the White Council being members so what would be the benefit?
And don't say "protection from the White Council". The Accords regulate the peaceful interactions between the nations and help define how wars are fought - the new group wouldn't be protected from the White Council any more than the Red Court Vampires were protected from the White Council declaring war on them.
Then there's the duel nature of the Laws of Magic. Break the laws and you get the Lawbreaker feat. Keep it up and you are looking at changing your aspects until you are a monster. That still happens even if the last Warden is dead and the White Council scattered - so there's no real advantage to starting a lawless group.
And unlike how South Sudan came to be, the White Council can't afford discord. It can't. What it can afford to do is send the Blackstaff to where the new group is meeting and have him collapse the building on them. Situations like that one - a group exploiting or hiding behind the laws of magic - is why the White Council has a wetwork man.
To sum up:
1) Any group of empowered mortals trying to get a seat at the Accords table is viewed an internal matter for the White Council to handle.
2) If it was possible for another group to get a seat then one would have - with the backing of the "enemies of humanity" Accords nations.
3) Getting a seat at the table won't give them anything they don't already have.
4) If they even try hard to get it, it's treason (see point 1) and just ask Morgan what happens to traitors.
5) If they try to exploit the White Council's own rules to get it, well that's why the White Council has the office of the Black Staff.
Can anyone cite anything in any of the books that even looks like it disproves the argument I'm making here? Because if all you have is "just because Harry didn't mention it doesn't mean it can't happen" then I'm going to counter with my "Harry Dresden - serial killer" argument.
Richard