Ever thought of reading this?
http://www.smogon.com/forums/showthread.php?t=3469098
Now, I do agree unpredictability will be her main game. The potential for a mixed, special, or physical set are all there. Thunder Abuse with Serene Grace in Rain sounds amazing as well.
Technically speaking, no one has broken any of those rules as of right now. The reason why those rules were put in place was because of the Therian formes being introduced and everyone cried UBERS. We are simply discussing if Meloetta is going to start out in UU or BL when it is finally introduced instead of having it BANNED to Ubers.
Yes, Meloetta is going to be slightly unpredictable. it can run a physical, special, or mixed set. It can even run a paraflinch set with T-wave/Zen Headbutt. Maybe even a Charge Beam sweeper set too. So yes, it has many options. The thing that hinders it is that on the special side, it has a meager 90 base speed. That doesn't out-speed much. If it wants to be physical, it needs to waste a turn setting up. I'm sure some people will be able to master the craft of using Meloetta to great results, however, many people will have a tough time figuring out whether to attack instead of switching forme.