Linus Torvalds has settled that whole discussion for the Linux kernel.
Thankfully his opinion about C++ is meaningless outside Linux world.
Windows started to adopt C++ on the kernel since Vista, you can make use of Windows Implementation Library, a C++ template library for kernel, drivers and userspace code. Just gotta to love that VC++ /kernel flag.
macOS with its NeXTSTEP heritage, changed from having Objective-C drivers on kernel space to C++ drivers in kernel space.
Then if you bother to broaden your horizons beyond FOSS UNIX clones, there are enough OSes already shipping C++ on the kernel.