A deal to merge the Big 12 and Pac 12 has fallen through. If the Big 12 and the Pac 12 merger/some sort of agreement didn't make sense, I doubt it would ever make sense for the ACC.
Oddly, enough, this is potentially bad news for UNC and the ACC. While the ACC has a great deal in place to keep the teams locked together, there isn't going to be much attraction from Pac or Big 12 schools to join the ACC. So what could happen is the Pac 12 will be poached for parts by the B1G and Big 12 (I doubt the SEC goes for them). That will likely beef both the conferences up to a point where there isn't much value in expanding more. When the ACC deal finally gets financially viable to break (assuming there isn't an agreement or legal challenge that does that earlier), the three main conferences will be fairly full.
It's hard to predict how things will look in 10+ years, but if things stay as they are now, any school looking to jump will have to bring HUGE value to the conference. Right now, that is really Clemson. If Miami and/or FSU get their act together, they then become at least as valuable as UNC, assuming UNC continues as a middling football school.
UNC is super attractive for many sports, but right now those are blips when compared to football. If conferences are fairly full, and UNC isn't bringing football revenue to match Clemson or another more 'traditional' football power from the ACC, they could be struggling to make an argument for entry into a conference.
Hopefully things work themselves out, but this could be really bad news for the ACC and its schools - and crushing for schools like NCState and the 'also rans' in the ACC.