Higher member capacity for PvM guilds
Current limit for members in a guild is 76. A guild which is active as a community can have real problems with this limit. And yes, you can kick inactive members, but that is sometimes not enough to make room for the new people. Also it is not that ideal if you have to kick people already after just a few weeks of inactivity...
Another consideration that I am well aware of: For WoE guilds, the discussion is the opposite. So it needs to be distinguished between WoE and PvM guilds..
I have no clue, if this is even possible to programm. But one idea for a solution would be: Implement a guild skill like "Vow of Pacifism" that increases the member limit with every point like Guild Extension.. This skill would in return disallow the members to enter castles during WoE hours.
Most bigger guilds (meaning the communities) consist of more than one ingame guilds anyways. To irreversibly dedicate one of them to PvM only shouldn't be problematic, if the member extension is wanted.