I've come up on this thread without reading much into it, but now that I've read some of Elysia's posts I think I know what she's on to. I think, an operating system that can actually fully isolate and protect process address spaces without the costs of hardware task switches. Potentially you can have more speed, security and reliability, instead of less, with all memory requirements, communications with other process and whatnot actually able to be better enforceable at runtime.
But if I read what Elysia is talking about right, this isn't exactly about running everything in user space. There's simply no concept of memory domains. Everything runs in kernel space. I think i did hear of these things before (and actually on these forums a long time ago). I did some searching on Google and came up with Microsoft's
Singularity project.