I was actually 100% serious... most games with a global chat system suffer because spammers can just clone accounts and keep spamming.
If you set a limit (say iron age) at which you can join the chat you force spammers to put in a lot of work to be able to enter the chat.
In age of empires you research a technology called "writing" that lets you see your allies bases and units. I was implying something like that could fit in really well with the current architecture of the game. Possibly being researched at the Alliance Gate (I had forgotten they didn't have the library then).