I like this idea... But realistically... I can't see them using it. Not to mention the fact that there is no specific "council" status in clans to separate for council chat. (not an official position to assign)
Also, underlining or bolding the chat in the "all" tab doesn't help solve the problem of knowing where, because not only does chat scroll quickly, the terms of use would have to be changed for silencing due to chat/ads posted in the wrong tab even once.
Lastly, other chat complications, such as the difference of chat viewing between devices, would also need to be changed. (iDevices, as far as I'm aware, only display about 2 lines of chat, androids up to four, and computers infinite. Feel free to correct me on that.)
This has some good thoughts to it, but it requires many changes to the game itself before it can be considered feasible. I'd give tentative support at the moment.