Well this is reportedly on the way. If this is accurate, I think it will be a smart move for Microsoft. Indeed I reckon if they price it correctly, they could make a nice bit of revenue from the millions upon millions of iOS users who are (still?) using Exchange at work.
Another alternative would be to make the app free to help support Exchange itself.
The offline mode sounds interesting. Will folk prefer to use the existing native email client though?
This fall, Microsoft plans to release two new native iOS applications on the App Store featuring the Metro user interface: Outlook Web App for Exchange 2012 users, and an updated mobile version of the Lync communications platform, AppleInsider has learned.
Microsoft is currently planning for both Outlook Web App and the new Lync to debut on the iOS App Store before the end of October, a person familiar with the upcoming software revealed. Both will be native iOS applications that render Web content with the same tiled Metro user interface style that can be found on Windows Phone.
via Microsoft working on new native iOS apps for Outlook Web App, Lync.