The BT may be interested in Kansas, but there is no obvious 16th team available (MO & ND are not practical at this point).
For some time, I've considered Colorado to be a possibility. 36000 students, pretty good academically. A new TV market. They can't be happy with the Pac 12 $ they're getting. Also no natural rivals in the P12. They probably would not come if offered, however, because of demographics and culture.
There have been recent rumors concerning Iowa St. I never considered ISU as a real candidate before because it adds no TV market. However, the focus on markets is changing as technology changes. Things like fan base, rivalries, and fit look to be more important than 10 years ago. Along these lines, see the article below.
I know, I know. Some of you are driving by here just to see if I have lost my mind. Let me say fir
hawkeyepodcast.com
Edit: Here are some ISU facts to consider: 33400 students, #118 US News. Pretty highly regarded in AG, the hard sciences, engineering. 61500 football stadium that dates to '75. 14500 basketball stadium that dates to '71. Iowa-ISU football---45-22 Iowa all-time. Iowa basketball---46-28 Iowa all-time.
I doubt anything happens till '24, when tv contracts expire for the Pac 12 & BT....it will be interesting to see if the BT adds Kansas and Col/ISU in a couple of years. Right now, I would think the BT would like to see TX & OK have to pay to get of the BT. If the Big 8 dissolves too quickly, that won't happen.