I don't see how it changes anything. The refs still have to place the ball based on where they see where the ball is at when the knee hits the ground. Then after everything is placed the optics tell them it is a first down or not. Really don't think this a big deal. Not until they have ground sensors sensing a knee sensor hitting the ground and a chip sensor that shows the entire size of the ball coinciding with the previous sensors will it make a difference.
Not sure blue font is needed... seems like a logical next step. Maybe several years away, but not inconceivable they develop "where was knee down" technology.
Also, the current use of optical sensor will definitely help for ball placement when "knee down" isn't relevant-- like when a runner is pushed out of bounds, or at the end zone pylon, as examples.