This is strictly for the attractiveness of UCF and USF for the Big 12 (as it's pointless to even consider them for the SEC or ACC, much less the Big Ten or Pac-12):

Advantages for UCF and USF: great locations both in terms of TV markets and recruiting; large enrollment schools that are growing fast; fairly good on-the-field track records compared to other G5 schools

Disadvantages for UCF and USF: arguably the most competitive college football market in the country with Florida and FSU being elite marquee programs and Miami being a top tier national TV brand (making attendance irrelevant with respect to Miami); very young FBS programs in a P5 world that craves/demands old school blue blood history even from weak programs (see Rutgers); real and perceived bias against "directional" schools in terms of branding; academic perception

Non-factor: It's irrelevant to argue that a G5 school would have better attendance or TV ratings by playing a P5 schedule because that would be true of *every* G5 school. Instead, a G5 school has to show that it would bring attendance, TV viewers and revenue to those *P5* schools as opposed to the other way around.

Now, I'll know we'll hear the arguments that it's hypocritical to use, say, academics as a factor against UCF and USF when you see a school like UNC systemically violating the NCAA's academic procedures... and those arguments are entirely correct. However, if you're a school on the outside looking in, it simply doesn't matter. Every argument that is used to keep you out will be emphasized much more heavily than any argument to bring you in. Simply being better than #65 out of the 65 P5 schools is NOT the standard being used.

Of course, all those points are moot if the Big 12 or any other P5 conference doesn't yield more per school revenue by choosing to expand. UCF and/or USF could go undefeated for the next 10 years straight and it wouldn't matter if that revenue equation doesn't change.