I'd much prefer WVU as the 16th than that set-up. The logistics of a Navy Georgetown hybrid don't really make a lot of sense. Is the money for ACC basketball, and other sports, better than the Big East pay-out? Does Navy football bring enough to the table to earn a full football share of revenue? Really the only way I could ever see it happening is if Notre Dame is adamant that they would only join based on Navy's addition, as well.
The WVU fan base turns out and supports their team and I personally think the ACC needs some more die-hard fans. I get people have this opinion that they're this hoard of uneducated people but it's honestly exaggerated at this point (it's not at the level it used to be where they lived up to the reputation). It's really not all that different than the portion VT's fan base that never attended the school. It comes with the territory of being the best college football team in any state. Adding any SEC team, outside of Vandy, would bring a similar fan base.
There aren't many programs available that bring enough viewership to justify adding them. Outside of the big games or involving the big teams, people are drawn to watch rivalries. The Backyard Brawl along with re-igniting the rivalry with VT will bring viewers. Even our rivalry with WVU resulted in our bowl game outdrawing a lot of other bowl games in 2018. A bad WVU team last year still drew respectable ratings. A pretty good 2018 WVU had solid ratings that year, even when being stuck on the black hole that seems to be FS1.
WVU lacks the big market and in-state population that is valuable for conference networks but they tend to bring solid viewership and are immediately a competitive team that bring with them some already established rivalries. A ND addition would cover most of that already though so I'd rather avoid adding one of the schools based on potential or their state population numbers only to hope they aren't a doormat, like Rutgers is for the B10. Cincinnati is the only one that makes a bit of sense but they are the back-up plan.