Many groups already do this.
For example, my guild has a forum and chat tools on our website. PSN and XBL also offer text based communication tools. There are other forums where people can make threads already for grouping, etc.
The problem is that in order to use these, you need to look away from the game. So, you either have real time text based communication, and are constantly looking away from what you are doing in game (regardless of the device, medium being used) or you lose the real time aspect and ignore text chat while you are playing, only checking on it periodically; which defeats many of the advantages a text chat system in game provides.
This is a work around people are already doing, and they are not happy with it (as you can see from the support for in game text chat).