I am not against implementing it. I am against implementing it myself because it's a pain in the ass to manage and requires way too many custom features to implement to a level people would even enjoy such as group banking. If a couple of close friends want to do it then they can do it unofficially. I also don't see group ironman as a highly requested or game-changing feature that would push anyone away from the server.
The server is open source, if you want to put in the dev time to add this gamemode, by all means go ahead. I'll accept a PR if someone else does it.