So lets say you predominantly use text chat because you feel more comfortable than talking to someone via voice.
You are in an alliance but are planning a betrayal. Or perhaps just want to talk behind the back of one of your crew!
There could be something you could add before you type, like a key you could bind or a grammatical symbol you could type before hand that will enable you to whisper.
Basically as long as you are very close to a person you could type it or hotkey and only people standing next to you can hear.
However they still is a chance they can if they walk by so it would be wise to check around like you normally would!
As for shout text chat. Basically the same but reversed. As we cant text chat and use the voice projector item, it would serve as a text chat equivilant.