A new MachineKit image is now available. While there are no dramatic changes with this release, pretty much everything got updated. There's a new kernel (-bone33), the latest Debian (7.3), and continued updates to LinuxCNC. One somewhat major change is switching from the xdm display manager to lightdm, which plays nice with consolekit so the shutdown/reboot buttons work, user-mode USB mounting works, etc.
There's no dramatic reason to update if your current system is working well. This is primarily a baseline build I wanted to make available before I head off and start seriously working with the joints-axis code on the BeagleBone for controlling the non-Cartesian 3D printers I'm building (a Mini-Kossel-Pro mashup, and Nicholas Stewart's Wally and GUS Simpson).