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Looking at the concept art for Z-Power Moves it seems like they're going to push these types of Z-Moves to have a larger effect on the trainer. Notice how after the attack is used the trainer is on the ground panting.
Z-Moves are probably going to sap Ash of his energy similar to when he used Synchro. If you notice in the anime Ash and Pikachu are no longer effected when using Z-Moves. They shake it off an continue battling like its nothing.
They're likely going to make it so that using an enhanced Z-Move is more risky of a move instead of something that can be used at any time.
Maybe the Z-Power Ring is what finally changes the Electrium to Pikashchunium, the enhanced connection between Ash and Pikachu and the ZP Ring causes it to change.