I think the PAC schools have to know a number before they make that big of a decision. Institutional changes rarely happen without gaming out all the ramifications. With enough unknowns, the tendency is to not make any decision.Could also be the Big12 removed a disadvantage. Seems to me it makes Pac12 & Big12 in equal position from a contract logistics perspective.
Both can negotiate separately with their current media partners and get firm #'s. If the Big12 feels it can get substantially more from ESPN/Fox great. But it may need to be significant to get Pac12 schools to jump.
IMO Fox & ESPN would value a combination of some Big12 & Pac12 schools the most.
I also think Fox values itself as being a West Coast based sports network and desired having Pac12 games.
I'd have to think the B12 has good information that they will get a significantly better offer than the PAC.
What would a PAC/B12 combination look like? Probably 12-14 schools, with 4-6 from the PAC and 6-10 from the B12? What would the difference in per school revenue be vs 4-6 PAC schools joining the B12? Who gets cut from the B12? Cinci, WV and UCF get you in the eastern time zone. Houston is probably the least essential of the Texas schools. Would one of the Angry 8 turn out a couple of their own, and who would that be? Iowa St, K-State, Kansas and/or Baylor?
I'd wager the difference between a PAC/B12 Frankenstein vs 16-18 team B12 is negligible. Besides, which party has the greater need? Does the B12 need PAC schools to be the #3 conference more than PAC schools need to not be in the #5 conference?