I think you should be allowed to type to each other when dead, however people are capable of flicker eye movement and reading text on screen especially for low res since it's bigger. I know about this because i can.

i don't support talking once dead however, low voice or not. It is possible to pitch your voice to a level where someone within 2 feet can hear you from the side but not from the rear. And marshalls can't hear everything. I know, I tested it hearing my teammate swear a few times but the marshall didn't, because background noise will break up the sound by the time it hits further than 2 feet.