I don't think anyone's arguing that Northern VA alone can carry the state... No one region can carry any state (with maybe 1 or 2 exceptions)... But it's getting to the point where democrats merely need to break even or close to even in the swing regions to win the state because NOVA is growing so strong. It's becoming the equivalent of NYC to NY State.
This seems spot on.
The only thing is that NoVA isn't as populous compared to the rest of Virginia as New York City is to the state of New York, which just slightly complicates things for Democrats.
Looking at recent presidential elections in Virginia, it seems like the outer NoVA suburbs and competitive counties in the southern and central parts of the Old Dominion are where elections will be won in the future.