I trained in Kyokushin karate for my first decade or so in budo. Since 1982, however, I have trained in a Wado-based style/school. Over the years, I've looked at, investigated, played with, and just plainly been exposed to various ashi- and tai-sabaki for the ending of Pinan Sandan.
Examples of ashi-sabaki: Turn: 180 degrees into either shiko dachi, kiba dachi, or neko ashi dachi. Shift right: 1. leap to the right by executing a left-right action with the legs (jumping over something on your right); 2. slide the left foot to the right foot, then step out with the right foot into kiba/shiko dachi; 3. do a step-slide (right-left) step, yori ashi, to the right; 4. Step right with right leg and pull left leg into neko ashi dachi (mirroring previous neko ashi dachi).
Examples of tai-sabaki: 1. stay erect in kiba/shiko dachi, executing punch over the shoulder to opponent's face, while smashing elbow backwards on same side; 2. same stance and posture, but this time instead of punching over the shoulder, the "front" elbow pins your opponent's arm on your chest, while the same elbow as before executes a smash to the back; 3. from the neko ashi dachi, bump/check with the butt/hip back into the opponent, turn the body slightly sideways, and execute the above punch/elbow smash to the back combination.
I have always thought of this sequence of moves to contain bunkai to an assault/grab from behind. Butt/hip checks, elbow smashes to the back, punch to the back, shoulder throws, hip throws, etc., can all be applications to the whole set of movements from the turn on.
As to your question regarding the open hand. I don't recall learning it that way when I learned it in Kyokushinkai. I'll check my '60s copies of "This is Karate" and "What is Karate."
Neverthless, you raise a very interesting point, though. Many historians have written that Itosu Ankoh sensei (who designed the Pinan series), was asked to produce smaller, simpler, and safer kata, to help popularize karate and introduce it to school-age childern. In doing this, it is said/written that he eliminated many of the more dangerous open-hand techniques, replacing them with punches, etc.
Please continue searching, and I would be very interested to know what else you find out.