I haven't heard this new rule talked about at all, but saw it in last night's Bills/Bengals pre-season game.
A QB who dives forward (without being touched by an opposing player) only gets his yardage for when he first touches the ground or his knee touches before the dive.
So, a QB who lunges forward from the 40 yard line to the 42, then slides out of bounds at the 43 untouched is only awarded the 42, but a RB/WR who does this gets the full yardage to the 43.
I can see this causing major controversy later in the year when someone like Russell Wilson or Tyrod Taylor runs the ball to the 3 yard line, dives - and without touching any defensive player - his knee touches when the ball is at the 1/4 yard line and then he slides into the end zone. This will be ruled that the ball is down at the 1/4 yard line instead of a touch down like it's been the past 100+ years.
Why does the NFL do this to itself?