Not sure how hard it is to create a team chat; for example type /valor and all those in team Valor will be able to read/see the chat. Might help to swarm certain gyms, help get pokemon etc.
This has been talked about, were not sure if doing it per server, or entire server across. You know having a couple hundred people in one chat would be impossible) so it would probably be per server. I my self have no idea how hard it is to do that either. But I'm sure once bugs are fixed and rolled out, and some more important things are added they will look into it.
Team chat would only work per server too; otherwise everyone will try and squeeze onto one server. (or need to figure out which server people are talking about; unless if it is a global chat a server number may need to be specified next to the player name)
Thanks for your suggestion. If you have any further unanswered questions please feel free to send me a message on the forums.