I guess that depends on where you draw the line at "kernel" and what you consider "unusual".

I study kernels for fun, so I've had a lot of opinions like that over the years, but none survived gaining more experience. For example, I used to think that the Windows NT kernel was a microkernel, then I thought that it was a hybrid, but now I know that it's actually monolithic. Likewise, I now understand that the major differences between the FreeBSD and DragonFlyBSD kernel are really just a few hundred lines of code, nothing major. But if you Google it, it'll make it sound like they're worlds apart.

Part of this is understanding that what people call "the kernel" usually includes a lot of things that, arguably shouldn't be considered part of the kernel proper. And a lot of the differences people cite between kernels come down to different message-passing architectures that are extremely interesting academically, but don't show up in real-world testing.

The sad part is, you can't reach this level of understanding though normal means, every source of information is full of half-truths. You have to dig into the source code and run these things on a bench yourself.