@atsync: I think you should try it out and see how it goes. Off the top of my head, I can see you will have probably some issue vs Curse (and maybe even non-Curse?) Ferrothorn. I was thinking maybe Heatran might give trouble too if it burns Cloyster (or Cloyster fainted already) and outspeeds Metagross. Similarly quiver dance Volcarona will be deadly too if Cloyster is dead already or sash is broken (without any Shell Smashes).
Of course, most of the time Cloyster will have one Smash by the time its sash is broken, so probably most of the time it's fine, but priority moves, quick claw, sand, focus sash, and brightpowder/lax incense will prevent Cloyster sweeps. Latios and Metagross are good backups, but plenty of things can still threaten the combo.
I'll be keeping this all in mind. I really hate Ferrothorn. I always forget to prepare for it. Metagross learns Hammer Arm at least, though Curse will definately be gay. The Heatran and Volcarona issues are situational though so I guess I can hope I'm not put in a situation where they are a problem? I'll be regretting this train of thought latter on I'm sure.
I'll try it and make changes when appropriate. I chose Latios and Metagross out of convenience (I already have them from other teams) so if I need to make new pokemon so be it.