Apologies in advance for a policy, rather than a programming question, but given the paucity of information available online I hope I can be forgiven for asking it here.
I think the policy around auto-renewing subscriptions on iOS may have changed recently, but it's tough because there's still a lot of older information and testimonials from developers out there. Marco Arment's blog talks a lot about the policy here and here, but those are from 2012 and 2013
As of now (mid-2014), from what I've been able to gather, the relevant policy has changed from this:
"Apps that use IAP to purchase items must assign the correct Purchasability type Appler In-App Purchase is currently an Auto-Renewable Subscription. However, it would be more appropriate to use the Non-Renewing Subscription In-App Purchase type. Auto-Renewable Subscriptions are intended for periodical apps, such as magazines and newspapers."
to this:
Apps may only use auto-renewing subscriptions for periodicals (newspapers, magazines), business Apps (enterprise, productivity, professional creative, cloud storage), and media Apps (video, audio, voice), or the App will be rejected.
So it seems like an older restriction that was mostly focused on periodicals has now been expanded to a bunch of other use cases. There are a number of public examples of apps like Evernote that have switched to auto-renewals.
Source: https://developer.apple.com/app-store/review/guidelines/