This is a big reason for our strategy at Edera (https://edera.dev) of building hypervisor technology that eliminates the standard x86/ARM kernel overhead in favor of deep para-virtualization.
The performance of gVisor is often a big limiting factor in deployment.
I read the thesis on arxiv. Do you see any limitations from using Xen instead of KVM? I think that was the biggest surprise for me as I have very rarely seen teams build on Xen.