According to people who have seen the latest OS X Server 3.1 Preview build 13S4122, the beta is much the same as the last release, which brought bug fixes to Server and Profile Manager.
As for Profile Manager, the latest build brings new "My Devices" portal access restrictions and device enrollment restrictions available on Users and Groups, as well as a feature that automatically retrieves an Activation Lock Bypass Code on enrollment of supervised devices.
The addition looks to be aimed at integration with Apple's new mass iOS device deployment management program, which the company revealed in an update to its website at the end of February.
Known issues include an issue where Profile Manager will stop working after an upgrade or migration from OS X Server 2.x. According to Apple, the problem does not affect upgrades or migration from OS X Server 3.0 or later.
Developers can download OS X Server 3.1 Preview build 12S4122 via Software Update or Apple's developer webpage. To test the software, developers must be running OS X Mavericks 10.9.2, which was released last week.