I'm absolutely loving malph atm.
You'd be absolutely idiotic to say that he loses some of his amazingness versus double AP but you'd be equally idiotic to say he's useless against double AP, just need to adapt the build.
The fact he has a 50% attack speed debuff built into his kit and an unblockable (bar Sivir, noct, morg and banshees shield) ultimate with fairly decent range means you should always be able to cripple the enemy AD carry.