Someone brought up the point of what if playoffs expanded to 8 teams. If they expand it would only be to 8 teams and would not be until 2026 as it is locked at 4 until then. Not sure how this impacts what likely would happen, but might open up one playoff slot to a non big 4 conference team. Hard to tell once the conferences consolidate to 4 - 16 team mega conferences. Big Ten and Pac 12 media rights are opened back up before 2026 and you know those conferences will be fishing for big fish before then.
Any expansion would be discussed and confirmed long before 2026. Look for that conversation to heat up in the 2022 time frame, plenty of time for teams to make decisions.
Who knows what will happen in 2025 though. The ACC may never get their TV network, and by then cord cutting will have had a significant impact on the bloated Big10, and SEC. It wouldn't surprise me to see contraction, or the content providers wanting "eyeball" match ups. By then, 8 more years of our model will hopefully build some better cohesion within our conference.