That support for iOS 5 is to follow that which RAC supports.

RAC 3 is iOS 6+. RAC 2 might also move to 6+.

But I'd be open to move to iOS 7+. If a user came along and said they wanted to use the library but needed iOS 6, it seems quite possible that `NSProgress` could be back-ported to iOS 6, similar to what `PSTCollectionView` to allow `UICollectionView` on iOS 5.