Modules would become even more powerful if you could edit the content of an existing module and have it update in all uses across all email messages.

Would come in handy when we have so many messages using the same modules. Like updating a signature block if someone changes job titles or phone numbers or something. Or updating the default transaction information across multiple segmented audience receipts.

That is assuming it's even possible... I imagine it is, but is likely involved. We use an email builder called BeeFree that added that functionality a couple years ago. Could be an interesting resource for your dev team.