From what I have read the expanded T4 will be open at the end of May, but I have not seen a date where they expect to move everything out of T3. For all we know on May 25 they will still be using T3 for their international ops.
Even once this move is made, domestic flights are still planned to depart out of T2, so your ATL flight (unless it is a widebody) will likely depart from Terminal 2 anyways.
If the expanded terminal 4 is open, I suppose you could clear security over there and check it out and then hop on the bus to 2.
Thanks everyone for your replies. One of the other reasons I picked JFK was the fact that my flight is on a reconfigured 763ER (76L? Whatever the subtype is with 36 lie-flats), which I have yet to try, so T2 seems to be out of the question. So the international widebody on a domestic flight should make up for any potential terminal disappointments
