I found this in wiki pedia on the 500 Linebaugh :
The .500 Linebaugh is a proprietary cartridge and thus has not been adopted by mainline firearms manufacturers. Currently no firearms manufacturers make revolvers specifically for this cartridge.
I dont think Ruger is going to pay a license fee when they could just as easy chamber an industry standard 500 S&W mag with good ammo and component availability. The Linebaugh is a .510 that is a good standard, but more for big rifles than pistol rounds.
For a revolver this looks like a world more practical than a 4.5 pound S&W with an ear busting muzzle brake. That is not my call, the world is what it is.