they have explicitly stated the builds will be roughly once a month i believe. Your (our) model might be added next, depending.
they have also stated that in the software development process they focus on a single platform so as to stabilize the code first without the variability with different chips. (All those eligible for the most part are Snapdragon 400 phones)
Eventually when they're happy with how its turning out, we'll probably see it on the S4's (920, 620...) and 800's. (M8, 1520)
It's not a rollout.
Also, I'm pretty sure the Preview for Developers is still around, so we have that.