We actually proposed this idea to the person from Apple who was dealing with us, and although he said he can not "pre-approve" anything, but this seems to be ok, and within Apple's guidelines:

1. Users pay $19.99/year for 100 GB for a plan that does NOT have iOS access. This is a PC/OSX/Android only App, that has nothing to do with iOS.

2. Users pay $29.99/year for "100 GB + iOS Access" plan. The iOS app will have an IAP for the "100 GB + iOS Access" plan, for $29.99/year.

3. We wont offer the IAP for 19.99/year for "100 GB Desktop only" plan, because that subscription can not be used from iOS anyways.

How are we offering such low prices? We have worked very hard to create very efficient storage and compression technologies. We are not using a third party cloud (S3), and have built our own cloud, ground up, which drastically reduces the price. We are not offering much free space. According to our estimates, upto 50% total space on Dropbox is used by free users. Basically, Dropbox is "taxing" its paid users, to cover the charges for free users.