I'd like to have all play modes from the original BS. Especially random and a proper forward-reversed mode where the first notes don't get hit twice would be really nice.
There is no "proper" ping-pong mode, but two types. First and last note repeat ensures the pattern length is doubled so to not ruin a pattern that is sitting in a structured song, whereas only hitting the first and last notes once means the pattern doesn't quite make double length reaching the beginning of the pattern a step short of double length. I have a few steppers and the ones with ping-pong tend to have either or, with the Keystep being one of the few with both (and only on the arpeggiator).