Trading wrestlers to a rival promotion which will depending on the wrestler that's traded could cause the ratings to go up or down on the show the wrestler was traded to would be absolutely ridiculous, why would either of them trade one of their stars to a rival promotion? certainly you can argue that like the NFL the teams are a rival "promotion" but in the end aren't they on the same show getting the same ratings? and not going under because the ratings go up or down as opposed to the wrestling world ? (I don't watch NFL, don't exactly know how it works)
But quite honestly, I think the idea of trading wrestlers between WWE and TNA to be an idiotic idea if I should give my honest opinion, and I don't see why anybody would want to trade the wrestlers they have under contract for one that could prove to be a bigger or smaller draw (if the draw is bigger, I don't see why the promotion that gives up the wrestler would ever do that, and if the draw if less, I don't see why the promotion that gets the wrestler would ever want him there)
While I do agree there's some TNA stars I wouldn't mind seeing in WWE (again perhaps, Kurt Angle definitely) I do believe it should come on the terms of the wrestler and if he even wants to work for that promotion.