The issue with a native iOS app is that Sakai is generally used by education institutions, and thus the range of mobile devices that students have is wider than just iOS. An app that was restricted to just iOS would be less attractive because it would be seen as limiting access to some. This is why I have proposed a cross platform app mobile app using PhoneGap which can target multiple platforms with the same application code.
We can also use the PhoneGap build cloud (build.phonegap.com)
We can certainly point you in the right direction about the Sakai RESTful API's if you are still interested?
cheers,
Steve