I can understand the desire to be creative and try something a little different, but the reason so many players have those group compositions is because they work WELL. You can make almost any kind of group setup work, but it may also be very challenging and might not have the same synergy and dps as a 5 shaman or 5 pally team.
My advice is to try anything you'd like, if and when you get them to 60 you'll know whether or not that team will be fun for you. (probably a lot sooner though!)