I actually have OGL content for 4E that includes guns and gun using classes, vehicles... it could absolutely work, and I do love the system. My problem with it is primarily its more niche nature, most 4E games naturally go for the traditional D&D playing stuff. This is a leap. And since my failed 'Star Wars/Ace Attorney' game, I'm a little reluctant to leap too far from what people expect from a system. ;)