As most altcoin algorithms are memory heavy, ASICs would not be faster then GPUs as memory speed would bottleneck device as ASICs and GPUs use same memory. Only gain from ASICs would be fact, that they would be more power efficient, but impact on mining would not be as near as close as it was when BTC went from GPUs to ASICs when we say massive increase in performance and massive drop on power usage at same time. And that is biggest reason why there are non and most likely wont be one in near future.