One of the key features of Windows 8.1 is the inclusion of a version of Outlook 2013 for Windows RT users. While that's a welcome improvement on the half-baked native Mail application, it does have a number of restrictions for enterprise users.
A major limitation is that there's no support for configuring via group policy. There's also no integration with Lync or Sharepoint, and most features that are included in the professional version of Office 2013 (including archiving and information rights management) are disabled.
Given that competing tablet devices also lack manageability features, this isn't a deal breaker, but it's something to consider in a broader RT rollout. Hit the link for a more detailed account of what's missing.
Outlook 2013 RT is here, and this is what you need to know [Office IT Pro Blog]