When I first heard about the Scarlett/Ripcord thing it was totally left field, as was the casting of Marlon Wayans as Rip. I watched more of the cartoon than read the comics so I was prepared for a Duke-Scarlett relationship. I thought Wayans was okay as Ripcord, his jokes weren't all that funny, but he handled the action scenes fairly well. I also found myself liking his pairing with Scarlett.
Watching the film, the Baroness-Duke thing, also left field, made Scarlett having a relationship with Ripcord more feasible/palatable. I knew a little about her having something going on with Snake in the comics, but in the context of the film I can see why she might be attracted to Rip.
He's humorous/charming, brave, supportive, and challenges her a little. He got her out of her comfort zone, he got her over herself. The film didn't do enough to build up a Scarlett/Snake Eyes relationship. Snake was a grim, cold fish, despite his deadly skills. When you put the two side by side, what woman wouldn't have a more fun time with Ripcord than Snake Eyes?