I know it's in Nightly, but wasn't it in Nightly 3-5 months ago, too? Shouldn't it have moved to the "next" development version by now, like Aurora or whichever is the next "more stable" one, if Firefox follows a 6-weeks development cycle?
Not every feature can be completed in a single six-week train, especially one as complex as rewriting huge chunks of a browser that was not initially designed with process separation in mind. :)
That said, we should have a go/no-go on Monday for uplift with Firefox 40. We're getting Very Close Now. :)
If we do the uplift, I believe the plan is also to hold there until we clear out a bunch of less-critical, but shipping-blocking bugs. So it might be on Aurora for a few releases.
