I think .45 Colt is, and will continue to be, a "niche" cartridge, like the .44-40, .32 S&W Long, and other basically obsolete cartridges that have just enough interest to hang on. The major drawback for SD and to some extent for HD, is that it is a BIG cartridge, made for BIG guns. Even in gun-friendly states, running around with a low slung six-gun like an Old West movie character is discouraged and most folks prefer to keep the hardware out of sight even if that is not required by law. (Yes, I know some folks claim to be able to easily conceal a .500 S&W, a Ruger SRH or a 155mm howitzer, but let's be realistic.)
Jim