Shortened and cut down responses. I highly advise reading the actual AMA, a transcript will be posted on Battle.net, but until then, there's this.
The AMA:
http://www.reddit.com/r/IAmA/comments/19sg1x/we_are_dustin_browder_alan_dabiri_and_david_kim/[1]
DB, DK and AD are who made the comment.
General
DB: SC2 dev team consists of 80+ Developers, hundreds of QA+ Cinematic+Other
DB: Not ready to give details on map marketplace
DB&AD: Did not deliver on promises of the HotS FAQ in terms of Arcade, and will be doing more work on it
DB: They would do polls but the results are never representative as most players don't use the forums
DB: A few developers working on Allstars. Most people working on Swarm, some artists have switches to Allstars with Swarm being finished, while campaign team has started work on LOTV
DB: They would not release the game if they don't think it's good
DB: No plans to go F2P as they can't find a design choice they would be happy with to make it F2P
DB: Reaction to b.net overhaul was surprising, people were way more excited than they thought
DB: We have not seen a decline due to the rise of "DOTA games", they don't see any threat. They are very different games with very different players
AD: Confident HotS launch will go smoothly, expecting "Over 9000" players within 5 minutes of launch
AD: Talking alot about improving the replay screen and how players can view and share plays. No time line yet
AD: B.net API and replay format specification is hopefully coming... eventually
DB: They would like to not patch the campaign if possible, if necessary, they will
Legacy of the Void
DB: Legacy of the Void is in development, Story, Scripts, and Missions have been started.
DB: Custom Campaigns support possible for LOTV
DB: They hope it won't take as long as HOTS but efficient and quick game development is not something they have been great at
DB: Story isn't set in stone yet, they have ideas how it'll end but no final answer
Multiplayer - General
DB: In-game unlockables are limited by memory
DB: Map sizes are much bigger than they ever thought it would be
DB&DK: They have an engineer working on making map-hacks more difficult but do not wish to talk about it for obvious reasons
DB: They will talk about the economy system, but obviously no changes for Swarm
DB: Stronger Team Colors had technical issues that would hurt lower end systems
DB&AD: Blizzard Time to Real Time is being worked on, but it was more complex than they anticipated
DB: The decision for 2 gas was to make SC2s economy more complex as they felt it was too simple with 1
DB: Everybody will see skins, but for players in esports settings, they can choose which skins to display
AD: They would like to continue adding AI builds in the future
AD: Not happy with Barcodes, as it defeats the purpose of GM (that being to be able to easily follow the best players), they are looking to address this but it is a delicate balancing act between privacy and being able to track players
DK: Balance issues could be fixed with maps, but not overdoing it is important
DK: Situation reports will continue
DK: Most tops pros focus on macro and require other players to create good strategies
DK: 3 base play on ladder is more popular than pros. They continue to talk about it but it isn't as major as people think
Multiplayer - WOL
DB: PvP and PvZ had issues in Wings due to the unit mixes available, thinks Swarm has addressed the issues
DK: The Queen patch was actually one of the best changes they made. They still feel like Hellions running in, killing all the drones, and the game just ending wasn't exciting to watch
DK: They tried air and semi-air based maps, but scouting is far more important than in Brood War so it didn't work well
Multiplayer - HOTS
DB: They tried Lurkers again in HotS, but they were not as good as they hoped, they were not as cool/fun/effective as the new units
DK: They are okay with Corruptors, it is not their favorite unit but it works well
DB: Community feedback had a massive effect on the Oracle, "basically undid out entire direction for the unit"
DB: It was hard to get good feedback from pros as they were often biased towards their own race, but David did find some pro players and casters who had more neutral views and formed relationships with them to get feedback
DK: Still thinks Oracle are unique despite losing the ability to harras without killing workers
DK: The goal for the Carrier is to never to be a core unit, but still able to come into play here and there
DK: Nydus worms changes were cut due to too much variety in lair tech for Zerg
DK: They want mech to be viable but not replace bio, feel like it'll be heavily tied to maps
DK: They don't think the Hellbat has many weird rules, other than gaining a bio tag
DB: Altering the core economy (3 base eco cap) would be a huge change and mean re-balancing the entire game
Esports
DB: Happy with KeSPA supporting SC2
DB: They will continue to promote barcraft
DB: A calendar won't be in launch but they will talk about it
DB: Esports is much bigger than they thought it would be, they expected 50 people in a room, not thousands
DB: Plans for 2013 and beyond not finalized, frequently talking to teams and organizers
DB: Esports is a big part of the development process
AD: Gameheart is very cool
AD: The customisable observer UI doesn't allow scripting, but they have some cool ideas for the future of it
AD: Reaction to the Custom Obs UI was a little surprising, they are glad we're excited for even the smaller features in HOTS
DB&AD: The Custom Observer UI shown in the eSports and Multiplayer video as an example, will be available with the HotS Launch.
DK: Maps on ladder could use a huge improvement, current plan is to work more closely with tournaments, not only meaning using tournament maps, but also creating maps with input from them.
Other
DB: Dustin Browder once beat David Kim, as David was reading e-mails during the final battle
DB: Activision have been very supportive of SC2
DB: Dustin Browder watched a ton of TLO, he enjoys watching Grubby and White-Ra stream. MKP is one of his favourite players to watch micro, and NesTea is still his favourite
AD: Alan Dabiris favourite players are Boxer and July.
AD: The team often go watch tournaments together, and have been to barcrafts in Irvine
DB: Browder thinks an RTS on a tablet would not be able to work at the pace of SC2 due to vision being effected by fingers
DB: Dustin is Platinum League - playing random
DB: Dustin wanted to release the game 1 year before release, but Mike Morhaime intervened and said they need more time
DB: Dustin thinks video games are the most complicated form of entertainment built by humans
AD: Alan Dabiri is GM on Korean ladder under the name "|||||||||||||||"
DK: David Kim doesn't just work on balance, he is a General Game Designer, working on all parts
(so now you can blame him when dying on brutal campaign too!) of multiplayer.
DK: Strength of reddit is the point system which makes important issues surface to the top quickly, it is one of the easier methods to gather feedback
DB: "Outbreak" is Dustin Browders favorite mission