Yes, he was serious when he went Shikai but he wasn't fighting at 100% because his Zanpakto wasn't in the mood to play. He has 4 shikai abilities we know of and he was only using 2 so he was fighting with 50% his power. If he used Irooni at the start Stark would have been finished because you can't hit nothing but the color you call and he only told stark the rules so the viewers (us) would know what's going on, thats plot induced stupidity. Cifer won't know the rules of his game, thus he won't hit Shunsui and hell get chopped on half like Stark did.