I think the standard for red card should be based on dangerous tackles and the standard should be the same regardless of where the penalty occurred or who committed it.
Penalty kicks should be awarded for any obvious goal-scoring threat whether intentional or not or whether they take place in the penalty box. Obviously, the closer you get to the goal the better the goal-scoring chance but marking an arbitrary box is silly. If the goal scoring chance was equal to or better than the chance of scoring a PK, then award it.
I feel like this would reduce diving where if you get the ball inside the penalty area without a clear shot on goal, there's really no reason not to dive. If you get caught, you get a yellow. If the ref buys it, you get at a minimum a penalty kick and possibly also a red for the opposition. Also reduces all those controversial plays on handballs on crosses.