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.
I'd say the limitation has been that sometimes we have to implement things by hand. But it has enabled us to do things that others can't achieve since KVM is a singular stack in many ways. For example, VFIO-PCI is largely the same across all VMMs, but we have true full control over the PCI passthrough on our platform which has allowed us to do things KVM VMMs can't.
The performance of gVisor is often a big limiting factor in deployment.