I just don' t see the B1G taking any of the current Big 12 teams. There is a short list of potential targets for the B1G and Texas is probably the only school on the list from the Big 12 but I doubt they would give in to Texas's demands. Others on the short list, IMO, are ND, GT, UNC, UVA, Duke, BC, and Vandy.
If the B1G could expand with 4 more teams, I would love to see Ga Tech, UVA, Vandy, and either UNC or Duke. Raid the ACC of their better institutions, make headway into SEC territory and leave ND on the outside looking in.