Available ahead of the weekend is the first public beta of VirtualBox 5.1. Highlights for this "minor" update to the software includes support for new APIC / I/O APIC implementations, support for Hyper-V para-virtualized debugging of Windows guests, more MMIO emulation work, the GUI has been migrated to Qt 5, improved VM GUI performance, and better Python 3 support.
Overall, it's a rather nice list of changes for VirtualBox. The APIC improvements should also help the performance of VirtualBox VM guests within certain workloads. There are also many bug fixes throughout the VirtualBox stack.
More details on VirtualBox 5.1 Beta 1 can be found via VirtualBox.org.