Just a fun post, what weird combination of firearm and cartridge combo do you wish existed? Examples: AR15 in 30 Carbine, AR10 in 6.5x55, MP5 in 45 ACP, etc.
More double action revolver options with conversion cylinders. .22LR/.22WMR, .357/9mm and .45Colt/.45ACP. There are the Ruger Blackhawks and Single Sixes, and I know Taurus has a couple options like that now, but I would like to see S&W and Ruger get on the ball with that.
Also, I would love to see pistols with smooth bore options as to allow the better use of shot shells. Freakin ATF takes the fun out of everything.