https://us.forums.blizzard.com/en/blizzcon/ TLDR - Blizzard CS says that's the best place to give Blizzcon feedback.

I ran into the manager of Blizzard's online Customer Service today at Blizzcon registration. This guys is passionate about helping. His motto is "We go where the players are". They try to see everything from Forums to Reddit to Forums to Twitter to Instagram to Forums to Discords, everything they can to be helpful.

He took my feedback about the registration process (mostly about Portal Pass and walking AN EXTRA MILE but that's not important) and said they would add it to their after-action list. BUt the important thing he said is that while they look for feedback and information from all formats, the forums are where they can do the most good and give the most help and find out the most information.

SO if you have feedback about Blizzcon, please, please for all of our sakes. For you. For me. For the others here. For the CS people who want to make Blizzcon better, please give your feedback on the forums too.

I met a half dozen of his team that really do want to help make our experience better. These are people who said their greatest joy in their job is seeing people excited at Blizzcon. So give them some good vibes and thank-yous and tell them what you really think. Politely. Constructively. In the forums.