The ACC can certainly improve a ton. Heck, just having FSU and Miami get back to being anywhere close to what they used to be would improve the perception of the conference by miles. It's hard to see the overall conference challenging the SEC on a consistent basis though simply due to the low fan support and money involved with many of the ACC schools compared to a lot of the SEC schools.
Clemson has proven though that an elite team can still succeed in the ACC and win titles even when most of the conference is down. As I said above, FSU and Miami could improve the outlook of the conference. Just look at last year with ND being part of the conference to see how the overall outlook of the conference was a lot different and we managed to get 2 teams into the CFP.
The teams at the top of a conference is where most of the hype comes from. The SEC is even down this year compared to some other years when you consider the ACC actually has more teams ranked in the top 20 than the SEC does. What the SEC does have though is both Georgia and Alabama in the CFP which makes the overall conference seem that much better.
TV money, and de facto backing by ESPN / Disney as THEIR conference, the SEC will still always be the 800 lb gorilla in the room. It just means more, to ESPN.
To me, when things will get interesting along those lines is when Darth Saban finally retires. Does Bama really try to poach Dabo from us, assuming Dabo is still here? Now, THAT would be one of those "seismic shifts" in coaching like we have already seen a couple of this year.
I think it more likely that Bama goes immediately back to being mere mortal with Darth hangs up his Dark Side helmet. That will cause a multitude of "ripple effects" that even ESPN with all their propaganda will not be able to control.