You are assuming that your OS scheduler is nearly at capacity, it isn't. And moreover your CPU is will spend most of it's life idle.
I could almost guarantee you this is not the bottleneck of any modern setup.
I can guarantee you that I have jumped over to my browser when doing a compile that is definitely limited by my machine. I'm ok doing this knowing that I will only take up so much work on my machine. I do not go off and kick off another giant compile at the same time.
Now, if the browser becomes more and more consuming, hitting my browser could get closer and closer to kicking off another giant compile.
I'm not necessarily against all of this, but I'm also not eagerly embracing more crap to slow down my machine for no apparent reason.