We're in the same boat...er, plane. Our trip is 7/30-8/7, so we grabbed our outbound flight when SW opened their schedule through 8/3. (That was on Feb. 18, by the way...) Now we're just biding our time, checking the schedule each day, waiting for the return flight to become available.
My guess is that we're still at least a couple of weeks away from the next Southwest schedule unveiling. And since the trip itself is still more than four months away, there's no rush for us to get things nailed down right now. This is just one of those little pre-vacation-anticipation things that helps build the excitement....
Good luck with your plans!