I'm very well aware that this isn't really what you were asking for, but it's interesting to note that it appears to be possible to throw a debian VM into bhyve and use docker CLI tools from the FreeBSD host system to launch docker images inside the VM.
Having seen the vast amount of pain Joyent went through with their LX flavour zones trying to get the syscall emulation right, and Windows having gone "sod this" and switched to an embedded linux kernel for WSL2, I do rather wonder if this isn't as good as it's going to get without an engineering effort by FreeBSD that could likely get better ROI focused elsewhere.
