There is very obviously an in-state need for a good connection between the state capital (Charleston) and the second-largest city (Huntington), and the state's large land-grant and research university.
Which would still exist...
I-64.
The "state's large land grant and research university" is in Morgantown, with Clarksburg just to the south. Pre-I-79, there was no good way to get from those cities to Charleston, while at least Beckley and Bluefield had "the modern two-lane highway" in the West Virginia Turnpike and I-77 took care of Parkersburg and that part of the state. I-79, even though it was a long time coming, filled the need to improve travel from the northeast/central (actual northeast is the panhandle that now has I-68) to the capital.
Would I-79 to Beckley be a good thing? As someone who traveled between Blacksburg and Pittsburgh from the mid '70s on, it would have been great. At first there were two alternatives to drive -- I-81 to Winchester, U.S. 522 to I-70 and on to the Pennsylvania Turnpike, then west to the 'Burgh or U.S. 460 to the WVA Turnpike to Charleston, I-77 north to I-70 in Ohio, then east to I-79 and home. As I-79 extended further into West Virginia it had potential, but for a while there was no good way to get from its end in the middle of nowhere to Charleston. Even when almost complete, it required using surface roads to get from I-77 to I-79 until that junction was finally completed. Once construction started on U.S. 19 from Sutton, the trip became a little easier (unless one got stuck in the wrong section of two-lane with no passing and slow traffic). It still took some interesting back roads to get from U.S. 60 to Virginia (I tried just about all of them) until the New River Gorge bridge was completed, and even then, it still required travel through Beckley to get to the Turnpike (another project that took a while, completing the short connector from Bradley to the turnpike).
Bruce in Blacksburg (but a native of the 'Burgh)