A chat is a must for any game involving an alliance/tribe/coalition. It helps build a closer community and a more rewarding game experience.some people play games not just to play them,but for the social interaction in the game and will play a game based on how well this interaction can be achieved.
Sure,you can use outside chat programs,but it is always easier to use an IN GAME system.
World and Tribe chats would work well together.most games you can turn one or the other off,or have an expandable chat box.
Having experience in other games of this type i firmly believe that Tribal Wars 2 would not be complete without it and would become "just another" game of that type.
I Hope the developers give serious thought to this as they have so far come up with a great game experience,this is just blunting the sword a little,lol