Hm, it does make sense if the Zygarde cells are life energy that can connect to this new powered-up move mechanic in the games.
It helps with the fact that Zygarde is the only pokemon whose base HP changes between it's forms. The more cells it's accumulating, the more longevity it'll have.
During the livestream, they mentioned the name "Alola" is meant to incorporate a meaning of a land that overflows with life force and supports various forms of life. You know how "Gigareki" was filed differently than all the other trademark names? Well, the greek word for Giga is "giant", the word Reiki is made of two Japanese words - Rei which means "God's Wisdom or the Higher Power" and Ki which is "life force energy". So Reiki is actually "universal life force energy."
And the fact that they mentioned that the starters and Iwanko have a "secret",well, I think Gigareki might be a new move mechanic where a fifth move could be facilitated by the diamond bracelet that the main players are seen wearing, giving the Pokemon an extra boost from the player. Considering that the topic every professor of a new region focus on is related to something introduced in the games that feature said region, this could mean that Kukui's interest for Pokemon attacks may indicate that the new kind of evolution that everybody is speculating about will grant Pokemon access to a fifth powered up move akin to what seems to be the case with Complete Zygarde.
Nobody expected Zygarde to have another signature move along with the Thousand moves, but lo and behold, here comes Core Enforcer. The animation suggests that this move is only accessible to Complete form, and the 10 and 50% won't have it until they transformed. I think Zygarde maybe the source of the natural phenomenon, and it seems that since the trainer is using these dance sequences that corresponds to the type of the pokemon, this is shown to be a more natural bond between trainer and pokemon than ME, which uses the lives of pokemon. PR is Groudon and Kyogre trying to absorb more power for their own advantages.
Complete form still carries off many aspects in the 50%'s design, which was based off an example of the Ouroborus in Norse myth,such as the chest-plate eyes,a tail, the red and blue appendages forms into snakes, and it's cry sounds like a higher pitched version of 50% form in the Sun and Moon trailers. The crown-like head is mostly the main control of the whole body. It has some sort of a third hexagonal shaped eye while the other two eyes don't have any pupils. It's as if 50% transformed into a perfect, ascended form. Even if the dog can transform into this, it felt better that 50% can transform. I guess there is a reason why in Japan it's called "Perfect Zygarde".