We seem to have very different definitions of simplicity. I don't consider even more loaded kernel than Linux currently is simple.

It used to be part of the kernel back in the day. It was called devfs. It was dropped because a userkspace implementaton is more flexible and easier to extend and tweak. udev also isn't the only choice, mdev also exists and works without running an actual daemon (there is a file in /sys or /proc which specifies a program to run on hardware events, mdev handles the event, then quits).

Of course, nowadays devtmpfs is also a thing, fully kernel space, but not at all configurable. Mostly meant for early user space like initrd and such. But if you don't need anything special it might work for you during regular use, too.