Why would they need to relocate more than 7 or 8 miles of US-522 in West Virginia? Dualize the rest. I also suspect that there is more local traffic on US-522 than we might realize. Accessing Berkeley Springs from the south is considerably less distance on the current route.
The concept I posted above from West Virginia was to relocate about 20 miles of the roadway, and dualize a little portion entering Virginia. It may be cheaper to dualize most of it, but I suppose their standpoint is creating a limited-access type highway instead of a dual-lane. West Virginia is more strict on access management standards than Virginia, who mostly dualizes
(which isn't a bad thing, it's just the differences between the state's standards) and I suppose relocating it would achieve limited-access better. You could also do this with dualizing the road, but then you'd need to construct frontage roads, etc. which may rack up the cost.
Most of the US-522 corridor through West Virginia also has more dense development along it which could be another reason.
That alignment connecting I-81 and I-70 would entail crossing the Potomac River valley and building a bridge over the river. Environmental opposition and permitting difficulty could be a major obstacle.
If the goal is to achieve a 4-lane US-522 to I-70, you'd still have to build a new bridge over the Potomac River, and expand the 2-lane US-522 heading to I-70 in Maryland, which is a condensed path, to 4-lanes involving another bridge being built over the Little Tonoloway Creek. You still have environmental impacts either way, but I suppose less.
Relocating US-522 works to, the I-81 / I-70 connector was just another concept that would primarily benefit thru traffic.