Clay.io has it's own set of issues with some features not even working in CocoonJS , never been able to make it work consistently with iOs and Android check this thread, http://www.scirra.com/forum/plugin-clayio-leaderboards-achievements_topic54357_page29.html , still keeping my fingers crossed that they will fix it.
I am not even worried about the performance when i said ".... Why not in C2 ?" i was basically asking whey the demos with features like "facebook integration" , "Rate the game" , "webView" all works why not it's been integrated through C2 with the CoocoonJS Object.
@Ashley, i am not even concerned about GameCenter at this point because even their demos are not supporting GameCenter, i am wondering why the existing features implemented by the demos are not implemented in C2 as said above.
I think u and ludei should establish a formal communication channel because you both are interdependent and will mutually benefit rather than expecting ludei to scan through the forum and reply.
I had been recently using email@example.com email to correspond , they seem to respond pretty well, i think you should try that and i am sure they will be happy to help in any manner.