Riot, you are going way too ham on these Gangplank nerfs
http://www.surrenderat20.net/2016/02/29-pbe-update.html?m=1
The gold plundered nerfs are probably justified and needed. The amount of gold Gangplank can stack up with this and the mastery bandit (which everyone runs on him) is absurd. In fact, every nerf so far to him has been justified given his power in competitive play. But these powder keg changes... This is a gutting. If you go through with these changes, you are practically deleting him from the game.
The thing you have to understand is gangplank often uses triple barrel combos to get off a reliable chain in teamfights, this change allows him to do this once every 14 seconds or so late game with max CDR since the current supply cap is 3 and it would take about 13 seconds to generate two barrels (22 for 3). Given the length of teamfights and the storage supply cap, this is basically an ultimate cooldown overall, which is completely absurd. Even if gangplank went with a 2 barrel combo instead of a 3 barrel combo, he'd still be unable to reliably chain and would have long down times in between combos.
You know what this change does? It basically turns him back into old gangplank with a fancy aoe combo he can use once in a teamfight. Yes his ult is more powerful but still, only being able to do this basically once in a fight is making him a walking cleanse with a targeted AA that gives him a Trinity proc aka old gangplank. And we know how bad that was.
I realize powder keg is an absurd powerful spell and currently it's arguable that it is completely broken. But the design is good and I feel this change is basically you conceding that you don't like this design. Instead of completely butchering it, why not change the way they work with armor? Or why not remove its power to crit and give it an AD ratio? There are several changes that you could make that are better than this. Even changing his max supply to 4 instead of 5 could be a reasonable change. But don't do this, the gangplank rework was a success and it's arguable he's just in need of a few changes, maybe even numbers alone. But butchering him this way is the wrong answer. It's way off base.