With the way college football recruiting currently works, WSU isn't going to be in contention for many 5-star recruits. The Cougars have landed one, ever, and it didn't turn out very well. For the purpose of this discussion, however, let's assume the system changes. David Stern takes over as NCAA president and dictates where players go.
Under this new system, WSU is entitled to pick any 5-star recruit they want. They only get one, but can have any player in the country, the No. 1 pick of the 2014 recruiting class. The question then becomes, who do you pick? The obvious answer is to take the best quarterback available. Teams with really good quarterbacks tend to be really good. However, in Mike Leach's system that may be a waste of a pick. The Air Raid has been extremely successful without star quarterbacks.
After watching WSU's offensive line the last few seasons, a better pick may be an elite left tackle. Someone to anchor the offensive line and protect the quarterback's blindside. Maybe you take an elite wide receiver since WSU will throw a lot.
I think you could make a solid argument for a number of possibilities, but if I had my pick I would take an elite defensive tackle. That may seem like an odd pick, but elite defensive tackles are rare and can have a huge impact on the game. Look at the impact Ioane Guata had on WSU's defense last season and he was hardly an elite recruit. Auburn was one of the few defenses to have success against Oregon in recent seasons and a big part of that was Nick Fairley dominating the line of scrimmage against the Ducks.
I'll take the next Rien Long, who would you take?