You could have a “nanokernel” which owns the ring buffers and the other kernels act as its clients… or for a “primary kernel” which owns the ring buffers and exposes an API the other kernels could call. If different devices have different ring buffers, the “primary kernel” could be different for each one.

That sounds like the Exokernel project. Notably different from a "multikernel"/"replicated kernel" design.