Right. I think the libdispatch has done a fair amount of harm to the platform because it made it feel like multithreading was easy, developers started using it without understanding what was going on under the hood and terrible performance ensued. This is the same thing but on steroids.
Having personally gone the way of the libdispatch since it was introduced in Snow Leopard, having written a lot of heavily async code, and eventually having understood the hard way that it could not work well without carefully thinking about threads, I am quite afraid of the long-running consequences of something like this.
My first advice to developers about multithreading today is: don't do it, unless you know you need to introduce concurrency and if you do, apply it with care. Most programs don't need a great deal of concurrency and most are not good candidate for it (because they lack long enough non-contended tasks to execute concurrently). This proposal will make everyone use concurrency and multitrhreading with no understanding of the implications.