Protection rings are a lot older than x86. They were first used on the Honeywell 6180 for Multics back in the 60s, and used in pretty much every sufficiently large processor. The Vax had two-ring layout, as did the 68k, so the seeds for OS development in the 80s were already pretty soundly planted.

The page faulting was also on older systems, because putting those things in hardware is a lot faster than doing those things in software, plus controlling memory access really should be a privileged activity. Interrupt handling is in a similar situation, and even there, you still need some process handling the interrupt vector table. It's possible to make most of an interrupt handler a user-level process through page table and interrupt return address hacking, but for the moment, it's unfortunately rare.

As for your desire for a replacement for one exclusive, reserved kernel mode, there have been a few OSes that have tried to break that pattern. OS/2 used Ring 2 of the x86 for drivers, but unfortunately that bit wasn't added to Windows when they were forking NT. Being able to put semi-trusted drivers in a separate area, and perhaps even a user session manager too, could allow for some interesting security experiments that don't rely on (para)virtualization.

Hardware-wise, it would be useful to have hardware contexts, like sparcs have, so that the group of registers a process has can be swapped in and out a lot easier. Context switching is expensive, and building processors that realize that the modern user tends to have more than one task running would be a pretty good performance win.