Southwest used to have some rearward facing seats in some classic 737s. I flew facing backwards and it was quite disconcerting on take off.
Some years ago I recall being allocated a centre seat in the second row of a 757 on a flight to Phoenix out of Orange County. Row 1 faced backwards and was empty, so naturally I asked the FA if I could move to the empty row. I was told in no uncertain terms that Row 1 had to be kept empty. "Why?" I asked. "You'll soon find out..." was the answer.
Sure enough, the max energy take off required of 757s out of John Wayne International - with its (seemingly) near vertical initial climb to the airfield boundary followed by throttle back to minimum power level flight to the coast - would indeed have made those rear-facing seats extremely uncomfortable, if not downright dangerous.