To be honest, not much.
There is a reason that coaches at ALL games cover their mouths and have players hold up towels to hide signals. It’s because sign stealing is very common and has been for some time.
The outrage at the Patriots is simply because they got caught, and the NFL is burying the case because they don’t want it to get out how widespread it is.
Just to be clear, signal stealing is not illegal. What was illegal was doing it via videotaping.
They can videotape the games - as long as the coaching staff doesn't use the tape during the game. They can use broadcast footage of the signals, as long as the teams don't do the videotaping themselves. They can take still shots of the opposing team at will. What they cannot do is the very fine point of one particular method of recording of one particular action...which rule the NFL Chief of Operations mis-stated to be proscribed only if the taping was viewed during the game (Bellichek says he never saw that "reminder" memo anyway, so it is only minorly relevant).