About GameCenter and Facebook integration, out next release will include a much more compelling social and social gaming API so you will be able to handle Facebook, GameCenter and Twitter with a single code. Hopefully this will help Scirra to integrate these features.
Scirra is doing a great job exporting to CocoonJS. Their update frequency and productivity is simply outstanding (we would like to be as productive as they are but we have many difficulties in the way: Apple approvals, cloud integrations/sycnhronizations, ...). We are going to try to improve our support for Construct2 engine and we try to help Ashley whenever he needs anything from us.