DING has only been in existence for several months, so there aren't any historical records.
I, too, would book now. SW is running an internet system-wide fare sale until 8/1 or 8/4 - can't remember.
I booked DH and my tickets for our 11/28 trip to MCO at $89/way from Houston (where we'll be for Thanksgiving). That's a pretty good price anyway (lowest DING fare I've seen for that route is $74), and I was concerned that cost-savings around the holiday might be few and far between to begin with.
Good luck!