Making use of Linux’s Kernel-based Virtual Machine (KVM) opens up new possibilities while users can still enjoy the VirtualBox VMM itself. The KVM support is part of the mainline kernel so there is less worries with not having to use the VirtualBox kernel driver, KVM tends to support new features quite quickly, and tends to be more actively developed than VirtualBox and is embraced by a range of organizations. Early users of this backend by Cyberus customers are said to be experiencing better performance too.
This is really interesting and great news. I use VirtManager and Boxes but find VirtualBox to be easier to use and configure.
Commercially, there are sometimes VirtualBox images available that cannot be used with QEMU. I think even Microsoft makes “test” instances of Windows available as VB images.
VirtualBox is cross platform. I teach sometimes and, while I am using Linux, most of the students use Windows or macOS. It is easier to create instructions and give demos that use VirualBox. This announcement will be great for me.