Well in Sin & Punishment you could run and jump and roll. It wouldn't have to be a strict rail shooter. I mean, yeah Contra had some freedom to it, but it was still a linear game. They're always redefining rail gunners. I mean, Star Fox 64 had the free roam sections. S&P had rolling, jumping, guns and swords, roundabouts, etc. And Panzer Dragoon had 360-degree combat. So it's not like a rail gunner would be particularly restricted. If they wanted, there's no rule that says a rail gunner can't allow backtracking.