I feel you are asking for way too much there. 78 will not be freewayed in our lifetimes...the gap you speak of is denser than where they are currently putting interchanges. Winchester has significant development, including residential, right up on it...expanding that would be both expensive and very impactful...including one of the MEM runways and 3 of the 4 north-south taxiways unless you just leave the existing tunnel as-is under those facilities. Shelby isn't much better than Winchester in that regard, with development right up along the road including houses, businesses, and a fire station.
The 2 miles of US-78 from I-240 to Getwell Road is not picturesque at all. The properties alongside the road are mostly commercial/industrial with a mix of convenience stores and other service businesses peppered in there. It's generally easier to buy up that kind of ROW than it is residential property. Since the surroundings in that area are already pretty ugly the option of an elevated freeway built over the top of existing US-78 might not generate a lot of resistance.
I think once all the other improvements are completed on US-78 to the Southeast of Getwell Road it will put more focus on that last 2 mile gap. I've seen dense, cluttered areas of property cleared out before. I lived on the Quantico Marine Corps base in the mid 1980's. US-1 going thru Triangle, VA looked a hell of a lot different than it does now. We're talking a night/day difference. Dozens of properties along US-1 were cleared to widen out the road and "clean up" the main entrance to
The Crossroads of the 'Corps.
The FedEx hub generates a great deal of traffic. It's a bit surprising Democrat Road is just a 5-lane surface street running through there. The railroad crossing, going over a busy double-track route, is at-grade rather than grade-separated. That must create some traffic headaches.
Winchester Road has a good deal of residential properties lining its South Side between the Int'l Airport and US-78. But none are high end properties. And the closer you get to US-78 the surroundings grow more industrial in nature.
Memphis is certainly treated as a red-headed step child in Tennessee politics. But doesn't FedEx have some clout? It seems like they might be able to lobby for various improvements, even if they're "spot" improvements targeting one intersection at a time. Such improvements can accumulate over time.