My favorite microVM discovery recently has been tools built around libkrun. See smolvm[0].
The killer feature still missing from microVMs for me is the ability to enable CUDA support without passing through the entire GPU. vfio is just too much of a pain and too limiting. Sometimes I want to use my GPU on the host. Vulkan works fairly well with virtio-gpu and Venus, but I need CUDA. Venus is also still missing some important things like accelerated video encoding.