It was obvious that piplup would not evolve.
Unlike Haruka's Torchic, DP has been giving off plenty of hints that it would never evolve, such as giving it a great personality and making it one of the "out of the pokeball" pokemon (although unlike pikachu, it was sometimes in it) and debuting prinplup and empoleon (its evolutions)to story's sub-characters. Also it even gave it a whole ending.
As piplup tried to explain something to Dawn in the first section of the episode, I was thinking of how meowth could resolve the situation if he was there, but at the end, he did his job well lol. Maybe too well enough to blow up their well-made prinplup mech, which I really liked. I hope TR will develop empoleon mech in future.
Platinum FC: 5241 7799 4194