It has enough to warrant a rural Interstate,
Less than 10K between Waverly and Windsor. Barely enough to warrant 4-lane. Not even close for a freeway-grade facility, let alone an Interstate.
it would connect South Hampton Roads to I-95 and I-295
Not much demand for such. Not to Petersburg. As I mentioned before, you'd have higher demand tying into I-95 towards NC, and the best bet for that is the US 58 corridor, not US 460.
Some sections of US-460 carry close to 20,000 AADT today. The corridor carries 3,000 to 3,600 large truck AADT.
Projected 2030 traffic demand is 25,000 to 31,000 AADT depending on the section, with 30+% large trucks. If they are going to build something, it should meet a 20-year design, and that would be a freeway.
To expound --
The corridor Petersburg-Suffolk needs at minimum to be a modern 4-lane divided highway. That would mean widening to four 12-foot lanes, adding 10-foot right shoulders, and at least a 12-foot flush paved median. Some sections currently are flood prone, and those would need to have the grade raised above the flood plain.
In order to match US-460 west of Petersburg and 4-lane principal highways in general, at least 4 and perhaps 6 town bypasses need to be built to provide true high-speed 4-lane highway service. There would be considerable cost and complexity to transition each of those bypasses in and out of the current alignment. The cost of simply relocating the entire 59 miles is not much more than each town having its own separate bypass.
It could be argued whether the 59-mile relocated highway needs full grade separation, but I believe that at minimum the most optimum design is to relocate the entire corridor. I would rather see them wait until they can afford to build it that way, than to build a lower design sooner.