On the KVM front within the x86 space there is now support for hiding nested VMX features from guest, nested VMX can now run Microsoft Hyper-V in a guest, there is support for more AVX512 extensions, and there is infrastructure support for virtual Intel GPUs.
The Intel virtual GPU work on that front is exciting with the pieces finally coming together. Already in Linux 4.10 is the VFIO mediated device interface being used by Intel's GVT plus the needed prep work within the DRM driver. It looks like Intel's getting very close to having GVT be a mainline reality, but I think there still are some needed DRM patches that didn't land yet so it might not end up happening until Linux 4.11 for having Intel virtual GPU support within VMs.
More of the Linux 4.10 KVM changes via this pull request.
Then with the Xen pull request there are various fixes, including for ARM/ARM64, and a change of maintainership.