Financially, they're still negotiating from relative strength. They earn more per school than the PAC does, and the per-school payouts are what matters. USC, UCLA and some combo of others likely raises the money for everyone, especially if whatever primary media partner greatly divests from what remains of the PAC. Where the additions bring the overall new sum to only break-even for Big XII schools, none of us know.
To be clear, I don't think anything is going to happen. I think USC is trying to apply some serious heat to Scott and other PAC members to figure **** out (get a better media deal, or give USC a bigger piece of the marginally better pie whenever we renegotiate).