Along other things, Alcast made this video that explains some things about update 25 and its very informative I recommend players watching it so you could understand the issues that went on and how the performance update worked in a way. While not helping out in certain areas.
https://www.youtube.com/watch?v=6Skd9aI1nvU
To my point I think its clear that the Server is just boggled down with calculations and well a lot of things like the ever growing collections system the number of pets, cosmetics and other things. New zones new npcs and code put in to bar those without certain conditions from entering chapter/dlc areas without the key code to open the gates. I'm sure that doesn't help things out either. One of the the issues they have seems to be with the Non Combat pets. But I do wonder if the collection system itself could be causing issues I hope not

But I can see how something like this could boggle the servers or even ones own performance if one has to many of them and I think these are issues that do have to be addressed as well over time if there is any issues in that front besides the pets.
Greymoor when it is released the code is being rewritten to how these pets are operated by the server I mean many of us including myself have some kind of non combat pet following them around at times.
Counting the uesp on the pets in the game tried to be accurate using a calculator.
There is if I counted them right around 318 pets, possibly even more then what is listed but its a lot of pets. 318 pets and say someone has every single one of them the server has to calculate all from what I understand they take up a lot of server space from what I'm gathering from their performance update webpage.
There are 184 costumes, 111 hats possibly more depending on the last time uesp was updated. Not even going to count the number of other collectibles there is so many of them. A lot of them from mounts to hair styles, to head and body markings and a whole lot of things. Hats Costumes plus the number of pets all that together is like 613 in collectibles and that is a lot of collectibles. Plus all the other stuff I'm sure it would be close to 2000 or even more collectibles and that is just a best guess. That stuff I believe is tied to each account so the server stores all that and well that likely takes up space too.
So the pet rework and given there is like 318 pets and the codes being reworked so the server can handle them better and they are being reworked to take up less server resources that should help with performance.
The other stuff they are doing that will help out.
Player Character Loading: We are making the player character loading process multi-threaded on the server to improve performance. Internal bug fixing is underway. This work is on track to release with Update 26.
Multi-threaded Fixture Creation on the Client: This work centers around how art assets are constructed and drawn on the client, ultimately spreading this work out over multiple cores. Internal bug fixing is underway. This work is on track to release with Update 26.
Fixture Creation: This work is complete and on track to release with Update 26.
Character Update: This work centers around how characters are drawn on the client, spreading work out over multiple cores. This work is complete and on track to release with Update 26.
FX Update: This work is complete and on track to release with Update 26.
Sadly by the looks of it they are not releasing the Aoe combat changes with Greymoor pushing it to update 27 so they can track down issues on the live servers. This being one of the biggest things they were talking about that would aid with performance.
AoE Ability Performance on the Server: This work focuses on making these ability types more specialized so that they are more efficient on server performance. The code work is complete – data work has been shifted to Update 27. The current focus is on tracking down current issues on the live servers. Note: The overall player experience for these abilities (damage/functionality) should not change.
Gist of it
The character assets and the reworked processes on the servers to aid with performance seems to be what will be the biggest thing along with the overhead work to make pets take up less overhead/resources on the server.
I think the Aoe work needs to be released and If they are holding it back to trying to see what happened with Block or other issues. Trying find or fix before they add it in or whats the deal, I can see that being a good reason for holding it back. The other stuff are doing with Greymoor should help at least that is my hope.
The Aoe work I can see being a big time thing that would help lesson strain of Aoe effects on the servers and that is vital for the game to have and that rework should be released as soon as possible. I'm still hoping the Aoe gets released with Greymoor I really do but that might have to wait till third quarter. If they can take their time and do it right it might even be better then if they just rushed it.
The one question seems to be will it work and will it actually help? Will their efforts actually bear fruit, even though I'm hopeful these changes will help question is by how much? Anyone think these changes will help at all any?