Ouch! Where are you getting your numbers? And what proof do you have that Va & VaTech are collectively more popular than UMd - I only see a wash. But then I also see other BIG schools with plenty of alum in the DC metro. I mean it's a national city, hell international.
I don't think the Big Ten Network, for example, is banking on just slivers of the Baltimore-DC metro. Foremost, they will likely push & secure the entire state of Md since the Terps are the state's sole flagship. The push for the DC market becomes more like you say, slice grabs, here and there.
But it would be a damn good idea for the ACC to get it's own network first. These suckers take time to get up and running. The BTN struggled at first and the Pac12 Network is currently working out many kinks, despite having very little competition in its own footprint.
I can imagine an ACC Network pumping throughout much of Va, but in NoVa and the DC CSA, it will face competition from the BTN, there's just not much to debate here. As for Lville, you have a UK issue - don't front. Lville is a bonafide crossroads city between the Midwest and South - Ohio River Valley - where terms like Kentuckiana are used - Upstater made this somewhat factual point.