User blog comment:Mineko Charat Lucky/Your champion now has Annie's Pyromania passive/@comment-7929684-20130513182253/@comment-8506165-20130514110646

For some time? His W passive scales off his AD and he has standard ADC attack range of 550. Sure, the rest of his abilities scale with AP, but look at Tristana, who just has an AS steroid and her passive to buff her range, with all her abilities actually scaling off AP, but no-one questions Tristana as an ADC. AD Kennen when built with a nice amount of attack speed is a very vicious character who can land stuns every couple of seconds and isn't just reduced to ult + Zhonya's + be mostly useless afterwards in teamfights ("I can't hit my Q and I'm OOE after one EW combo").

I don't know that I'd try it at high-level ranked play, but that's not the same as "not viable".