The BT has always - ALWAYS - acted to do two things: be the richest and restrict competition (always to get richer and get more awards). That's the reason for both the unofficial Michigan-led boycott of ND and bribing the Pac to close the Rose Bowl. The BT DNA says that with Texas and OU off the board to the SEC, the only league capable of being richer than the BT, the BT will act before too long to try to get into the ACC and the South.
I doubt that the SEC will sit back and allow the BT to just keep trying to lure ACC teams and thereby get planted in the South. So I expect the SEC, at some point no later than its first whiff that the BT is active, to make it clear to UNC and UVA that if they do not wish to be in the SEC, the SEC will take NCSU and VT. And the SEC also would take Clemson and FSU, to keep the BT out of the deep South.
Any UNC or UVA fan who thinks his football team will be relevant even 2 years after it joins the BT and its in-state rival joins the SEC is a damned fool.
The SEC will stress that.
UNC will hold firm to do everything to save the ACC, but if Clemson and FSU are leaving for the SEC, then ACC football will be dealt a death blow. They simply cannot be replaced, because they have the most football history and they have the two largest fan bases.