If he's really worried about leakes he could also just tell them all the new concepts rather then actual cards (maybe with a few fake examples).
After you've got that coded it can't be more then a day to implement the actual cards, and perhaps a couple more to test it all.
(ok, that's the last assumption I'll ever make about goko code)
It wouldn't possibly do the trick for the AI. I mean, let's say the set is Intrigue. You explain choose one/two and action-victory/treasure-victory and pass and name a card and cost-modifying. They can get some of the code to handle those things up and running. But that doesn't set them up to have good AI for Pawn or Great Hall or Masquerade or Wishing Well or Bridge.
I don't know if Jay is worried about leaks or not. Goko leaked something, that is where the worry would come from. Jay was displeased. But obv. it's good to have the set come out online the same day. And it's hard to say just what the effect of a leak is, especially a late leak like this would presumably be.