NetBSD's NVMM may be the best target right now. Or HAXM. Both are
slower moving targets than KVM which changes *a lot* due to being
Linux specific. Note HAXM is around 80% the performance of KVM. Don't
know specs of NVMM but it has a few more advanced features. I've yet
to see a truly successful KVM port to another OS so I'm not sure it is
a good target, Solaris/Illumos has had one before but it quickly
became outdated and basically unmaintainable. NVMM does use some
specific internals of NetBSD to limit memory use so this would be one
aspect to consider compatibility wise.
Current versions of QEMU may not be entirely stable also on Haiku so
that would be something to fix also. You could probably get around
some of this by just running console only with no graphics.
https://www.netbsd.org/~kamil/asiabsdcon2019.html#slide25
