Huh...apparently to them, I-581 isn't an Interstate. Funny, last time I checked, it was designed, built, and signed as one...
As for their claim that it could become I-73 with even a short extension, they're a bit off. FHWA requires a logical and significant termini for new Interstates...for the most part, another Interstate, an NHS route, or a major city/installation. Aside from VA 419 (which is still in Roanoke County), there's nothing along US 220 that would meet that criteria until Martinsville.
In other words, local officials blowing smoke because they don't know any better...