It looks like this is no longer a rumor and it is true that Texas and Oklahoma are quite far along in their negotiations with the SEC.
Here is a ESPN article confirming it.

https://www.espn.com/college-football/st...-texas-sec

Texas and Oklahoma did not show up on the conference call, so it looks like they are quite far along in the process.

The ACC can take action and try and get a school or more from the Big XII as they will be seeing a big drop in revenue once Texas and Oklahoma leave. I wonder whether the B1G is trying to get in there and negotiate with Texas and Oklahoma. They probably could offer the same or possibly more than the SEC and they have a lot better academics than the SEC. Texas cares a lot about academics but i am not sure about Oklahoma