PvP Battle Arenas
On the subject of the PvP arena, the developers made it very, very clear that they want to keep the PvE and PvP games separate. Each skill has a separate data set for PvP and PvE, which may include tweaks to cooldowns, damage, and so on. In addition, Jay Wilson very emphatically stated that the team will never nerf a PvE ability because of PvP. The team also confirmed that there will be no PvP stat similar to World of Warcraft's resilience. They also confirmed that they have no plans to implement dual skill builds for PvE and PvP. The feeling they have is that a good PvE build should also be a decent PvP build, and vice-versa. It's also true that Diablo 3 is much more alt-friendly, so they're also assuming that a lot of people will just have a PvP character and a PvE character.
Finally, the team emphatically confirmed that there are no plans to support Esports play for the arena system. On the contrary, they plan to actively avoid the Esport moniker. Games like Starcraft 2 had to sacrifice a lot to become Esports, said one team member, and the Diablo 3 team just isn't interested in making those same sacrifices. They don't want their balance and design decisions to become slave to the Esport, and they want to give people the option of building quirky characters and esoteric builds. Clan and guild support is still under discussion as a Battle.net feature, though. It's also worth noting that there will be no PvP in the PvE game. If you want to PvP, you'll need to head to the arenas. That said, if you head to the arenas as a hardcore character, and you die, your character is still done.
A few players asked about plans for an endgame. The team admitted that they hadn't really solidified their plans yet. Part of this is because they need to see how people play the game in the beta in order to understand what they need and want from an endgame. You have to game before you can endgame, in other words. They did mention that they want to cater to as many types of players as possible, even PvPers, and that they wanted to avoid the Diablo 2 boss run phenomenon if at all possible -- if you like loot runs, they say, you should be able to get loot from running the game normally. While multiplayer modes like Capture The Flag and DotA-style combat are not completely off the table, they did emphasize that they want to stick to the core gaming principles of the Diablo series at all times, and they would not implement any gameplay modes that violated or drifted from that.
Boss fights, said the team, will be an extension of core gameplay. One of the team members said that they're looking to make them 50-percent Legend of Zelda and 50-percent Diablo 2. Zelda has simple, straightforward boss fights that still fit specific themes, and they'd like to emulate this in their own fights. When asked about resistances, they did say that they're making resistance scale with monster and player levels, similar to defense, so we shouldn't see arbitrary resistance reductions at higher difficulties. They also said they no longer plan to make monsters immune to forms of attack. However, they specifically left the option of fights that require resistance stacking on the table, noting that such tactics are a pretty classic part of end-game fights in a lot of action-RPG games.
The team also answered a few questions on how the economy will work in the game. They noted that gold simply became so plentiful as to be useless in Diablo 2, and that they're actively trying to avoid this in Diablo 3. To start, gold will drop much less often that it did in Diablo 2. There will also be a "salvage" option for magical items, which will let you break them down for crafting components instead of selling them. The services offered by the artisans themselves, such as enchanting and gem de-socketing, should also create a money sink. Finally, the team is building the system from the ground up to be incredibly resistant to the item duplication bugs and cheats that plagued Diablo 2.
In addition to the straight up economy improvements, the developers also want to make trading between players easier. They've already built a basic trading UI pane where people can put items and gold in a window on one side, and see what the other player is offering on the other side. They're also considering other solutions to end chat channel spamming and special games created just for trading. Finally, your stash will be "massive," reported one team member, and there will be a shared stash to cut down or eliminate the need to "mule" things between characters on the same account. In addition, all of your characters should be on the same account, as the team plans to make any character cap so high as to be nearly unreachable, and there is currently not plan to ever delete your characters.
Odds and ends
The team answered quite a few other miscellaneous questions as well. One questioner wanted to know if they would consider adding WASD movement support. He was afraid of clicking to attack and accidentally moving instead. The team said that they'd actually tested WASD movement and found it limiting and clunky, and therefore had no plans to implement it. But they did mention that you'll be able to hold the shift key to stand still and avoid accidental movement.
We also will likely see the fate of the old Diablo 2 playable characters and many of the locales. (We already know, of course, that the Barbarian male will be the same one from Diablo 2). The new PCs will all follow the same story progression (and aside from the Barbarian, both genders will have the same basic backstory); but there will be different class-based flavors to their interactions with and reactions to story events.
The developers also reiterated their dedication to fighting bots and any 3rd-party actions that they feel threaten the integrity of the game. The new Battle.net, noted one team member, contains a lot more tools to fight bots both passively and actively as well. Also taken off the table was the possibility of 3rd-party UI mods. The team noted that while UI mods work for games like WoW, they also bring an added level of complexity and often force the developers to balance their game around them; and again, that's not something they want to deal with, not to mention they don't want to make the game that complicated.
Finally, someone asked the ultimate question, the one on everyone's mind: Will there be a cow level? The team told him to check the Diablo 2 chat gem.