The thing that replaces the old memos is not email, its meetings. It not uncommon for meetings with hundreds of participants that in the past would be a simple memo.

It would be amazing if LLMs could replace the role that meetings has in communication, but somehow I strongly doubt that will happens. It is a fun idea to have my AI talk with your AI so no one need to actually communicate, but the result is more likely to create barriers for communication than to help it.