The designers came up with it. Artistically they wanted to do something new and nothing that fit into the current Diablo world, so they made a new and unique creation.

Originally Heroes was just a mod, what they really wanted to do was make it its own game, so we didn't want to touch maps in the Diablo/Warcraft/StarCraft universes in order to make it stand out on its own. Now that they have carved out some of that world it is okay to visit older franchises and explore how they manifest. Something that is immediately noticeable as Diablo but not two things you would see together in the same map in that game (the Heaven and Hell aspects).

Currently working on other maps that features the Heaven and Hell tileset. They wanted to keep working on that tileset because its so cool it has another map's worth of things they can do.

Examples of this being used in the past are Cursed Hollow being built off the bones of Dragon Shire so they will continue to try to reuse pieces in the future but spin them appropriately.

There is an ongoing evaluation of the talent systems, especially on the generic ones that are usable across many heroes. The team is working on giving each hero more a unique kit and custom talents instead of using the same over and over.

Expect to keep see developers continue to play with these, some are real changes that may happen some are not—this is constantly in development.

The artists try constantly try to push silhouettes on all heroes to keep them as unique as possible. When trying out new things, such as like Betrayer Malfurion and traitor Illidan there will be overlap because they take cues from each other, there is a clash in the lore when these things happen. The more skins the game has and the more heroes they have the more difficult it will be, and will be hard to keep super unique as it grows.

There is no real filter, in the future the goal is for more funny skins (like Bikini Stitches). If there are five skins they would like three to four of them to be serious, cool skins and then one funny one, around that ratio. Most of these will be cool concepts but there is a place for non-serious silly things.

The most important part is they want to stay true to the characters, so some characters lend themselves better to being portrayed in silly ways and some will be mostly serious and badass.

The problem with that is many skins are only good in memory, a lot of the stuff people want are images that aged terribly. For example the Butcher from Diablo 1, that dude ain't scary anymore, we only remember him as being badass because it was 15 years ago.

For iconic stuff, ie the Amazon from Diablo 2 they can do skins that match it and where they can they want to hit iconic classes but don't want to go too overboard with it. In some sense its almost cheating because there are so many old characters they can take from.

The designers approach it trying to fill voids that the existing character sheet always has, not necessarily by class. They are trying to make them as unique as they can, so the flavor is different with each Assassin or Warrior, and that's by design and will continue with new characters.

This tileset was very difficult art-wise because it is two in one, so there are new things they haven't revealed that will come out, some nods and Easter Eggs, that sort of thing.

In my notes I wrote "ETERNAL CONFLICT. HEAVEN AND HELL." there in caps but I'm not entirely sure why. Consider it a mystery of the interview.

The first time it will be playable will be in the test realm, June 23rd. If that testing goes well then it will go live the following week.

They made a note here that there are so many different things like this going on internally its hard for the developers to keep track of where it's all at.

The art people and design people will go back and forth as they progress on each hero, its very give and take. For example Thrall originally was a healer, but it didn't feel right because he is supposed to be a badass and he was healing standing around in the back. As the story goes they made him into Rehgar and made Thrall the current Earthshaker version that is in the game, so the design swapped it out and was reused.

There's a long back and forth in all cases, the process of making a hero is more smooth now so they know how the art design comes along with the cool design hero. A really cool art idea can influence dramatically design and design can influence a cool art idea. They are all prolific designers/artists so there are literally hundreds of ideas if they need to fill a void.

All the time. "We release the game so the community can show us how to play it."

It's very hard to design against that kind of thing, you can never be perfect which is why there is constant ballance and they keep iterating (Heyoka note, Blizzard loves using this word) on it constantly. They have a strong philosophy that the game is never done, they are launching because 'its ready' and they will never see it as finished. There is always the opportunity to look back at things and change it and make it better, chances to create opportunities and see how it goes.

The challenge now is that unless something is totally broken, there's a tendency to want to tweak things but sometimes its better to leave it alone which is hard to define. Players definitely show possibilities of what can happen out there. "Game feels like it was developed concurrently with the community". That process seemed scary, because Blizzard doesn't normally do that. Exposing something so new and valued, shows how strong the team is and after so many years of StarCraft II they feel good about their ability to balance (Samwise looked at me here and said not to bring up Swarm Hosts).

There is every intention of doing it, the genre spawned out of custom maps so they want to put the tools into the community's hands. Currently they are not actively working on it.

Note: this was one of the big selling points of the game when they demonstrated it at Blizzcon 2013, but what is currently stopping it from becoming reality are legal concerns regarding licensed content and a free to play game.

The only supported ones are the ones in the observer mode, like the nuanced views you can see in various broadcasts. Anything that actively modifies the live game, even for display changes, steps on portions of the terms of service. If there is specific feedback regarding the UI and its many revisions they listen and try to improve.