Well, their best dressage pair would still need to have minimum requirements in order to start. Still, I can't see any nation for whom such strategy would pay off. Maybe USA or Switzerland, as their best jumping combinations right now are not that great in dressage, but it's debatable.
I'm guessing that selectors will completely ignore dressage form while picking a travelling reserve. So this could open the doors for someone who would never be considered before, like Imogen Murray & Ivar Gooden of Great Britain, who often complete the event on their dressage score of 38-40...