There have been architectures specifically designed to support some form of IPC or other directly between processes without going through the kernel, and thus w

There have been architectures specifically designed to support some form of IPC or other directly between processes without going through the kernel, and thus without having more overhead. But those are a bit esoteric. The Mill is one, that has been in development for a while, but its company hasn't published much lately and its current status is a bit unclear. It would have had something very similar to Spring/Solaris "Doors" in hardware, where the caller could have passed temporary permissions to memory ranges. A "kernel" would have been a process like any other, just with more permissions.