I've seen several stories posted in 2014 that Apple looked like they were going to allow developers to generate promo codes for in app purchases.
http://www.macrumors.com/2014/05/15/developers-promo-codes-in-app-purchase/
But I haven't seen any evidence of this. I have a free app with a subscription model using non-renewing subscriptions to access the data.
I would love to be able to offer a free trial of a couple days like Android IAP allows so that users can see what is to offer, or barring this, a promo code to a subscription.
From what I can tell, Apple does allow trials for auto-renewing newsstand apps, but ours doesn't fit that.
And somehow EA got permission to give out IAP promo codes, but us smaller developers don't have that option.