It will be great if that actually happens. I'm not down on the idea as an addition to the arsenal; I'm just pointing out that it's not as generally applicable as people might think. User-space I/O is another one of those ideas that has come and gone many times over the last few decades. This time it will find some applications, to be sure, but there are also good reasons why most people will probably continue to be better off sticking with the in-kernel implementations.