Ken Null has made something like that for years: an upside down vertical shoulder holster. I'm not certain that he uses Kydex, but it was some sort of molded plastic. I'm afraid that the model name escapes me.
[This message has been edited by Daniel Watters (edited August 23, 1999).]
Also, the SafariLand "Gunquick" is an awesome shoulder rig, IMO, which has a polymer setup holding the pistol, and black leather straps. Good price, and no other shoulder holster will give you a faster draw.