Could the balance of good and evil belong to a single pony? If so, would balance be maintained, or fail bitterly? Can we really trust anypony to wield such power?

Too late. Somepony already has this power, and the emotional turmoil it causes is weighing heavy on his head. How long before he snaps? One was sure it would never happen, and perhaps she would've been right if not for a single shadow Equestria had thought dead.