Something as simple as this would work fine:
![Posted Image](http://i.imgur.com/tK6Kn.gif)
As it is, 4-mans and pugs are often working at cross-purposes because 4-mans rarely type and pugs are blissfully unaware. Knowledge of the communication landscape in a game would go a long way towards shaping it.
This is useful for a variety of a reasons, particularly to pug players. First and foremost, it shows which players on a team are likely to be operating cohesively, and thus which group to follow and support. Offensively, it shows which enemies will be a threat, and what level of coordination can be roughly expected.
The general situation report effect is also not to be underestimated. For example, since players on TS rarely communicate in chat, it's common for “that guy” to begin pug-herding, only to lead his flock to certain doom because half his team is actually a 4-man and has its own ideas. Things would go differently if that information was available. In addition, if a drop turns out to be 4+4 vs 8, it really is quite reasonable that this might encourage the pug to communicate more in an attempt to not die.
The benefits are subtle, but important. The fact is that at the moment you just don't know, and so players simply assume a situation and do their own thing.