Recently, I had the opportunity of watching naihanchi kata being performed as a two-man kata.
I know that chinese/american kenpo under the late Ed Parker used a two-man kata in their training.
That Hsing-I, southern mantis, and the like often use two-man kata. Reason being, is that it allows the student(s) to better understand some of the applications within their kata.
Some years ago, a friend of mine once commented that most of the karate/kung-fu styles of the past centuries often used two-man kata in their advanced levels of training. When I asked why it wasn't used anymore, the only reply was, "the old masters took A LOT with them to the grave. Only now are we starting to see what was lost/leftout."
Here's hoping that someone with a similar interest post a video link of other katas being performed as two-man katas. That maybe with a little experimentation (i.e. trial and error) someone may re-discover some of the missing two-man versions of such kata as:bassai, kusanku, chinto, rohai, sanchin, seisan, etc.