I have no real idea when Prime will ship.
After v3 shipped, it was around 5 weeks before Prime was available if I remember. It could be more or less this time, not up to me.
The dev priority after a major release is dealing with high priority bugs for the paid versions (appropriate).
If history repeats itself, we'll see a 4.01 version and then Prime will follow that.
That said, nobody knows for sure, and for free it's out when they get it done.