If we went down this road, I think it would be best to follow Jagged Alliance 2 as well as UFO: Aftershock and give everyone the entire skill list, just with different values (effectively enlarging the already existing stat screen). However, in these games there were some dependencies between stats/skills, for example both firing accuracy and medicine are related to manual dexterity, while dodge is related to agility... I doubt we could have this skill system without general stats. The X-Com model doesn't need them, because there are no real skills nor stats (only a clever mixture of both).