The holy grail microVM for me is one that can properly share a GPU across VMs, similar to what you can do with containers.
Shout out to https://smolmachines.com/ for supporting Vulkan over virtio-gpu/Venus. Currently the best implementation I'm aware of. Unfortunately my use case is running a full desktop inside the VM, and streaming it out over something like Sunshine/Moonlight. For this you need GPU rendering and video encoding. Venus rendering works, but you have to pass the frames back and forth between the host and the guest multiple times which is inefficient. Also Venus doesn't support video encode as far as I can tell.