Setting aside the clan size problem, which, to Fizzer's pov is probably just a quality of life - minor issue that a very small but vocal percentage of players cares about, I would tackle this from the perspective of profit, which consists of 2 factors
a) coins - direct profit
b) engagement in the game - indirect profit through ads, membership etc
I think common goals and more interactive clan pages with stats will help tremendously for the latter, and most likely motivate a lot of clanless people to join communities. So I see this post as a community problem and not a clan wars problem, like a lot of messages said.
Having more quests, levels, prerequisites, achievements and so on to keep players engaged is sth every game does nowadays, and while it can get overwhelming, it's probably the only way to increase indirect profit.
So, where there is will, and money, there is a way. And I think these can be found. Fizzer has also consulted players in the forums for changes in the past, I suspect he also has consulted or shared for testing privately specific players as well. The playerbase can actually help in the overall idea of what changes need to be done (not the actual implementation of the idea / coding, though).
The biggest problem I see with revamping clans and their sizes is dealing with the fact that you've already revamped them once and, as of today, there are clans with infinite size and clans of the size of 40. If you change it a third time, then do you have 3 different types of clans? the infinite, the 40s and the 60s lets say?
You can't really message all the clans with >x number of players and tell them figure out a solution till the 1st of December of 2024 when I'm putting a hard cap on 200 players and if there's 240 of you, then 40 random will get kicked . And you can't really disband clans or delete clans.
If we had a rough realistic example maximum of a community at 100 people, there's 15 clans with >100 people currently and 4 clans with 80-99 accounts, with most of them being straight up inactive. A rough solution for this would be, in my opinion: (take a deep breath here aight I just thought of this, I might have not thought of sth)
1) clans with <40 members -> we don't touch them. they transform into newly bought clans of 40 max people
2) clans with >40 members -> lookup how many active members currently (warzone class and idle, over last 2 weeks or month). get the number of the ones that are active (x). If x<40, then the clan is untouched, and transforms into a 40clan member. The inactive members of the clan are not kicked, instead they have a label that turns their name to italics and writes in a parenthesis inactive. If and whenever they get back online, a pop up message hits the screen about the changes to clans and they will be kicked by the clan automatically in 24 hours, unless the clan frees up space
3) for clans with >40 members and >40 active members, you make mirror ghost clans.
What is a mirror ghost clan. For example, the world league
https://www.warzone.com/Clans/?ID=251 has 162 members and 51 active members. You message the clan members some days/months before the change and tell them, the old world league clan will be archived in a way that all 162 of you will have access to the clan to see its forums, and the cw stats will be there as well, but on 1st of december of 2024 you'll be kicked. You cannot participate in any competition with that clan as it is archived, you just have manager rights that give you access to see whatever was happening there (not to delete stuff). And you give the actual clan/its managers or its creator, a new clan, with the old name, with all the old cw stats and forums, but tell them look guys, basic clans are now 40 people, your achievement points add up to 45 people, you have 51 active people, find a solution for it. Again, the other 162-51=111 inactive people are still in the clan as inactive and will get the pop up message when they become active again.
Seeing
https://wz-clans.5smith.ru/, there are 16 clans with >40 active people (with fivesmith's activity metric) and if the coin cost for the size of clan from 40 -> 70/80 is reasonably low, then those communities would opt to just pay up the extension and keep their community.
The actual problem is only 6 clans out of the 825 clans in warzone. And to that I would say either pretend like it's not a problem, or find a way to have a new tier of players in the clan, called "Reserve Members" or "Spectators" or "Community Members". There can only be up to 40 (or idk how many players the clan has paid coins to have maximum), but there is an extra infinite space for reserve members, that can participate in forums and the chat, but not in any way play for clan wars or get any idle rewards from the clan. Coiding wise, this sounds like a nightmare, but it would preserve the community of the clans with so many active members.