Mystery Interstate Corridor #1: I-75 Cleveland east to the North Carolina line. Tennessee sent a revised request list shortly after their submission and this corridor was removed. But for a fleeting moment, Tennessee wanted to connect I-75 to Asheville NC. There was no corresponding request from North Carolina. This corridor, along US 64-74 did get designated as part of Appalachian Corridor K.
Mystery Interstate Corridor #2: I-24 Jasper southwest to the Alabama State Line. There was no corresponding request from North Carolina. This corridor, along US 72 did get designated as part of Appalachian Corridor V.
Mystery Interstate Corridor #3: I-155 Dyersburg to I-24 Clarksville. This would've followed a lot of US 79's corridor

By 1970, two more interstate requests had been submitted, neither of which ever came to pass either...

Mystery Interstate Corridor #4: I-55 at Crump Blvd. through downtown Memphis, then east back to I-240. This was the Riverfront and Northwest Expressways. A small bit of the Northwest Expressway was later built as TN 300 (future I-69). Between I-55 and I-40 would've been feasible for the Riverfront Expressway but north of I-40 would've taken out a lot of buildings.
Mystery Interstate Corridor #5: The Central Freeway in Chattanooga. Per this 2014 article, this would've run from I-24 near the Rossville Ave exit and followed the Central Ave corridor, then crossed the Tennessee River to end at Hixson Pike. It would not have connected to US 27 or TN 153. Chattanooga requested this interstate from TDOT in 1964.