I was talking about the 5-1 codeset, the latest one.
For everyone's reference:
Shield stun: The lag you get stuck in when an attack hits your shield and you can't do anything, even grab.
Shield drop: The lag you get when you just let your shield go normally. It was very short in vBrawl, and long in Melee, and is somewhere in the middle now, toward the shorter end. This lag does not apply to shieldgrabbing or jumping OOS, because you don't actually drop your shield to do these.
You couldn't shield drop -> punish anything in Melee, but shieldgrabbing and SH aerials OOS worked just fine for punishment. In vBrawl, and to a lesser extent in Brawl+, people rely on shield dropping to punish everything, and to do things like nade camp with Snake, and to dash cancel. But in Brawl+ you can dash cancel with crouch, so it's not as big of a deal for that aspect. Adding more shield drop lag would definitely change the way you have to play, and you would have to use more aerials OOS instead of shield drop -> ftilt or whatever, but I personally think that would be a good change.