Nice fresh idea! I would not use it exclusively for opening training, but whatever works for your target group. Could be fun for younger players I guess. A few problems I see with this approach:
- When doing the exercise I was basically only looking for small changes from the previous diagram. I mean, for me it did not matter at all that I was looking at a chess board. It could as well have been a series of paintings (with incremental changes) or anything else. If people solve it the same way as I did, I doubt that they get much out of the puzzle for chess.
- I found looking through nine diagrams already quite time consuming, so I guess getting very deep (say 20 moves) is not very pracical.
- Including side lines seems impossible unless you create a puzzle for each side line, however in that case you would lose the connection between them (i.e. that at move x you have options a, b and c...).
- IMO, beginner players should focus on learning general opening principles, the reason behind making those moves and typical plans in certain pawn structures. Your approach seems to train learning lines by heart, which I don't find useful, because they'd be lost immediately once they are out of book.
Perhaps puzzles like these could be more useful for tactics or for basic endgames!?
Or perhaps, for slightly advanced players, it could be useful to have something like this, not move-by-move, but only showing relevant positions (tabiyas) skipping over intermediate moves.