While impressive that the optimal can be proven, I feel like the example puzzles here aren't ones that are particularly hard to find solutions for (when move count doesnt matter). I'd be interested to see at least one example that has a lot of tricky dead states that would act as traps.
This was a coursework problem in my CS course, back in the day. For larger canvases, the state-space blows up and it gets slow/intractable to solve.
Imagine providing AI with ability to poke around a large bank of gridbased game problem instances. Ask it to solve them and learn from them and then generate new problem instances.