The only possible play I see for the PAC to take somebody like SMU would be that SMU is willing to take a massive paycut for years, probably below what they even get from the AAC.
There still is some value for the PAC to maybe get into DFW market due to old TV media and to have a central time zone presence. Let's say it raises their total media contract value from $250 to $270M. SMU (who currently gets $7m/year in the AAC) takes $5m/year for 5 years, then become full members after that. Even in a case similar to that, which I think is optimistic for the PAC, only nets the existing teams $1.5M extra per year for the first five years.
I think for even the PAC to pick up G5 schools they would have to be in big markets and have some decent value in terms of inventory (most notably time zone expansion) AND those schools would have to be so desperate to get into a "power" league that they are willing to take a paycut for quite a few years from even what they get from their G5 league.
I guess I see there as a tiny window where a PAC expansion with MAYBE a couple specific G5 teams MIGHT be worth considering. I see no scenarios where it makes sense for the Big 12 to even consider any more G5 teams.
And listening to these old media dinosaurs talk about value of schools and conferences is hilarious. They've been so wrong.