[fulafel]

There are well known open source microkernels, like Minix 3 and L4. Probably not that attractive.

Why something hasn't been done is always a hard question to answer, since to succeed a lot of things have to go right, and by default none of them do. But one thing is that microkernels were more trendy in the 90s - r&d people are mostly doing things like "the cluster is the computer", unikernel, exokernel, rump kernel, embedded (eg tock), remote attestation since then (I'm not up to date on the latest).

[KMag]

Thinking about it a bit more, QNX clones might suffer from something akin to second system syndrome. There's a simple working design, and it likely strongly invites people to jump right to their own twist on the design before they get very far into a clone.