I doubt there will be an end to the big bore revolvers. They seem to be too...iconic? I own a S&W 500, and my father owns a 460, and we both really enjoy shooting them. They great fun, and are always great for friends to try out and see what a large bore revolver can do and whether you like it or not, they draw crowds at ranges.
The down side for me is the cost of shooting them. I reload, but the components are still more expensive than say a 9mm, or a 44 mag, or 357/38. I would shoot the big cannons much more often, if my wallet would allow for it!