No mention of Cloud Hypervisor [1]…perhaps they don’t know about it? It’s based in part on Firecracker and supports free page reporting, virtio-blk-pci, PCI passthrough, and (I believe) discard in virtio-blk.
We do, and we'd love to use it in the future. We've found that it's not ready for prime time yet and it's missing some features. The biggest problem was that it does not support discard operations yet. Here's a short writeup we did about VMMs that we considered: https://github.com/hocus-dev/hocus/blob/main/rfd/0002-worksp...
[1]: https://www.cloudhypervisor.org/