[snaky]

Universal kernel bypass for IO? Does it imply every userspace program should know how to communicate with every kind of IO device? No block layer? What about memory and caching?

[dooglius]

Userspace libraries (which userspace programs could choose to use or not) would presumably be available.

[pnako]

That's not a bad idea. You'll need some sort of mechanism to make sure they don't step on each other's toes, but otherwise it's a sound concept, not unlike MS-DOS.