Personally, I would like to see (hear) some of the King Biscuit shows from yesteryear.  Charlie Daniels Volunteer Jam VI (hopefully all 8 hours) was an excellent show, broadcast both live, and later on King Biscuit.  Molly Hatchet's King Biscuit show (circa 1978) was excellent.

And, something that probably doesn't exist, and doesn't really fit the format of Wolfgang's Vault.  It would be wonderful to hear something from Buddy Guy's tours of Britain 65-66...where he showed the future "guitar gods" (Eric, Jimi, Jeff, the two Peters, etc) how guitar should be played.