I took some time to find unknown opcodes the client can possibly sent.
I found a few, for example an opcode sent by the client when he receives a new spawn (player) with an unknown guild id. Normally all guilds and their ids are sent upon zoning, but if a new guild is created meanwhile the client does not know anything about the guild (name etc).
I also found a client command i had forgotten about or never used anyway, the /channel command. Apart from the server side filter command this command enables you to turn off the specific chat channels like gsay,ooc,auction,shout,ooc etc. The client can inform the server that he wants to either turn on/off a channel. I identified the requests from the client, we only need to add the filtering to the server which shouldn't be hard.
= 10020min (167h)