The 6-year media rights idea is a decent starting point for an exit penalty, but it does not seem sufficient to really deter the two big $$$ schools, which are the schools the conference really needs to anchor the TV deals.
Just picking a number for a talking point, say the TV money is $20 million/yr. That would put ISU AD revenue somewhere around $60 million/yr. There is likely no way ISU could afford to leave even a year early, so the deterrent works for a school with revenue like ISU.
A school like UT, on the other hand is a different story. With AD revenue of around $150 million, they could easily swallow a $20 million/year penalty, and they could do it for several years if need be, and still be ok. OU AD revenue would probably be around $110 million with the TV $$$ figure above, and they too could probably stomach a year or two of lost TV money if they really wanted to go.
IMO, the only really meaningful exit penalty that would equally effect all schools would be based on a percentage of AD revenue. Any team that wants to leave pays the conference 30% of their AD revenue for two years, or some such thing.
I will be shocked (but happy) if the conference adopts any type of exit penalty that really deters UT or OU from leaving.
The way I understand it is if Texas were to leave for the PAC-12 within 6 years, the Big 12 would still retain the TV rights to show football and basketball games and collect the revenue. There is no conference out there that would take anyone from the Big 12 because of this which is why signing away media rights to the Big 12 is even more iron clad than any amount of exit penalties.