My comments are completely unrelated to the 9th SEC conference game. I don't think ESPN would pay more for that game even if they were flush with cash. Even if it stays at 8, there is enough SEC content for ESPN to just ignore the lousy non-conference matchups.
Yes, ESPN/FOX were willing to pay decent money to the B12 for their content, but that just made the content problem worse, as it greatly reduced their need for even more content. Look at the networks one by one. ESPN certainly doesn't need more content with the ACC, SEC and B12. Fox has plenty, too, with the B10 and B12, and if they wanted more content they would just low ball the P12, which they still may do. NBC and CBS do not want as much sports content as ESPN and Fox which are sports oriented networks, so what they picked up from the B10 plus ND for NBC is plenty.
I believe your point on the "zero sum game" is backwards. No conference is going to add new members, no matter high profile, without first having an agreement with their broadcasters. And broadcasters can only handle so many high profile games without competing against themselves. The latter includes their streaming services.
I agree that Friday night and Saturday night games are in the future, and possibly conference semi-finals, depending on how the new 12 team playoff format pans out. But first dibs for these critical games goes to their current partners.
I will close by repeating the point I made above. At some time you reach the point where you are broadcasting/streaming games that compete against yourself. This is not an acceptable long term plan. For streaming to actually have an economic impact on conference income, it has to happen without reducing broadcast income i.e. moving games from broadcast to streaming, and the new money must come from new players, such as YouTube and Amazon. So far the non-network streamers have not shown any willingness to compete against the big boys for this content. I will reiterate another point I have made previously. The cable providers also provide a major portion of the internet delivery services on which the streaming services are dependent. This gives the cable industry the leverage to affect the effective prices consumers pay to receive streamed content.