I like this idea a lot. In future, players can choose there bot classes in unranked/private matches. But for leaderbord matches pier4r's suggestion would challange even the most experienced players, due to it's unpredictable nature. I'm gonna vote for it. ;D
/edit: But it kinda defeats the reason behind unlockable bot classes. Why would u have to unlock them, if u can't use them as you want? 馃