Castrandom always "worked" but as far as I know it still choses from any spell listed, not any available spell listed, so it doesn't skip spells on cooldown or that can't be cast. Oatboat's castrandom is all Arcane Shot, so I don't really know how that's different from /castsequence Arcane Shot, Arcane Shot. Unless it's just another attempt to get around Blizzards MoP macro changes.