Pokémon Z-A is an interesting concept. I don't know enough about the game to be hyped for it yet, but I've been quite worried about where they could go with it. I've thought about this, and from what I know my worries stem from one particular thing that would be heavily prevented if this following desire becomes real:
I sincerely hope the Kalos trio
don't get
any new formes or additional members of their group. I hope the game handles the trio in a story with them all just being the way they already are. This game is only taking place in Lumiose anyway so there's less of a chance Gamefreak would pull off anything extreme.
Why I feel this is complicated. Say what you want about the amount of presentation Xerneas, Yveltal, and Zygarde had in the games, but I
strongly believe the way their formes were developed was perfect and the way they were portrayed in lore and/or gameplay suggests they were meant to stay as is by the time Gen 7 rolled around.
Let's start off with Zygarde:
Pokémon X and Y introduced Zygarde at just its 50% forme. It had dex entries stating it had a secret power to use sort of as a last resort. This "secret power" was later first revealed in the anime to be a forme emphasized as "Complete". It is when all the Zygarde cells needed to reach its ultimate forme have collected together.
In Pokémon Sun and Moon, you were tasked with a quest to build this Pokémon fully from scratch. You had to collect individual pieces of it from all across the region and combine them together to access
every single forme of this Pokémon from
beginning to end. We had to construct this thing all the way from scratch and see through every stage of this Pokemon for it, from 0 to 100%. Not just in Sun and Moon either, but now in Pokemon GO and emphasized by Pokemon Masters EX. It would be incredibly frustrating to discover there was some secret 75% forme it could access midway through when we had to explore the development of this Pokemon's formes from beginning to end across multiple Pokemon games.
Edit 1: Even the anime made this sort of development too.
To follow up on this, I'm re-iterating that 100% forme is also emphasized as
complete. When
all the pieces of Zygarde gather together. Only to be accessed in very rare circumstances as a final resort. It was also used as a reward for completing Zygarde's development all the way through in both Pokemon Sun/Moon and Pokemon GO. It would be incredibly disrespectful to every single one of those players who liked this and even disrespectful to Zygarde itself for there to be a higher forme than this. Especially all the sudden years after its complete forme was emphasized as complete. Not to mention, its complete forme was never even used in a story yet. There's no harm in the game focusing on Zygarde transforming into just Zygarde-Complete at highest.
Judging by the logo itself and how it's made, I'm in heavy belief that the "A" resembles Zygarde-Complete itself, as it looks passable as that letter and far from the letter Z overall. Zygarde-10% has a Z-like shape. Zygarde-50% makes the Z a lot more clear. Zygarde-100% abandons the Z entirely and becomes more humanoid, and almost like an "A" like shape. Not to mention the hyphen could indicate that whatever "Z" is would go into "A". "Z" was always portrayed as Zygarde-50%. It could easily be Zygarde going from 50% to 100%; from Z to A; from Z-A. The name itself most likely indicates that this game would mark the end of something and a new beginning (likely an era), but it could also be used to emphasize Zygarde itself, especially with how they formatted its logo.
Ok right here on this post, I looked into the logo and found a huge discovery.
View attachment 610540
Notice the head. Pay attention to its head.
View attachment 610541
The head is pushed further down its body. The tip of its body is kinda like a new head, but sharper and pointier.
It also ends up with a tail that extends past the shape its body is trying to make. The tail is behind its legs. This is a given, but a very critical detail to note here.
If Pokémon tried to continue on its route to make its Kalos legendaries designed to resemble letters, the Zygarde-Complete forme looks more like it resembles "A" than it resembles "Z".
The face of Z is below the tip of its body and the tail extends past the shape it's trying to make.
The face of "Z" is below the tip of "A". The tail of "Z" extends past the "A".
View attachment 610542
You may now see the connection.
For Xerneas and Yveltal:
Xerneas and Yveltal are portrayed as eternal beings responsible for maintaining nature. They are from nature, they influence nature, and they maintain nature on their own. Xerneas and Yveltal have appeared as the physical formes they always were since the beginning and are frequently known to shift between formes already. Xerneas goes to sleep as a tree, then awakens as the way it is. It has a dormant form for storing energy, then an active form for using said energy to battle. It already has a dedicated appearance for battling and a dedicated appearance for retaining energy, so there's no new one needed. Yveltal's a similar case, with it becoming a cocoon while it's asleep but part of Yveltal's entire point entails it not storing energy, so it doesn't have a dormant form. I am against the idea of them getting some sort of mega forme or complete forme because Xerneas and Yveltal are actually already incarnations of said energy themselves. Mega Evolution energy already derives from them and they directly have the power to make Mega Stones a thing. Their powers to influence Mega Evolution are also expressed through Fairy Aura and Dark Aura respectively. Zygarde-Complete's dex entries also suggest that Xerneas and Yveltal in their regular formes are not much weaker than Zygarde-Complete itself. It would break the significance of Zygarde-Complete being above Xerneas or Yveltal if Xerneas and Yveltal got Mega Evolution, Primal Reversion, or Complete formes. Zygarde has a Complete Forme because unlike Xerneas or Yveltal, Zygarde is a bunch of smaller entities made up. It wouldn't make sense for Xerneas or Yveltal to get a Complete forme when they are one whole entity each and it wouldn't make sense to get a mega evolution or primal reversion when they are the very incarnates of nature's energy themselves.
These three getting new formes would break so much of what Pokémon has already established for them throughout media in ways far beyond Primal Kyogre/Groudon and Origin Palkia/Dialga. Especially since they aren't otherworldly entities from dimensions unsuitable for physical reality and aren't entities with known objects that never got utilized until their remake/premake.
A new Pokémon added to the group would also be immensely bizarre. There's no reason for something as significant as a major legendary to have not been recalled or featured in the games the rest were at all and no reason for Pokémon to start breaking past the cycle of 3. Shoehorning a 4th member in out of the blue would make the development of this group far more questionable than any group had ever been, with no telling of what makes it "complete".
Some people speculate the "A" could be Arceus. A being Arceus would be harmless but with the "A" following Zygarde's color scheme and being directly connected to the "Z" in both logo design and wording (the hyphen), it's almost clear that it's indicating a transformation from Z to A. "Z" was always portrayed as the 50% forme. The Zygarde-Complete forme never had much said about it but mysteriously strays from "Z" in shape entirely.
I might edit this later or make another post but that's all I can say for now. The formes for this legendary trio are already perfect as is, will always hold up for PvP battling (they already have more consistently than any other trio in the series bar weather trio), and giving them something new would most likely be a huge retcon that'd ruin any special feeling towards how they were portrayed before this game came out.
