Official Blizzard Quote:
There are no skill trees any more. Skills are still tiered by when you can buy them (essentially a level requirement) but there aren't any trees, it's one big pool. Before this game even reaches a beta state there will be hundreds of people playing it internally, and most likely there will be builds that are developed during that time. But the game is specifically being designed in a way that skill progression is as much of a choice as possible. There will always be builds determined to be 'the best' as long as there are choices and options. Making every skill and every pathway perfectly equal would mean watering down skills, making bland options, and overall homogenizing the classes and skill abilities. So it's a trick of balancing unique and interesting and fun skills while also ensuring that no matter which ones you pick you're not totally gimped. I also want to point out that skill runes can have a fairly dramatic impact on how skills function (and even look) so builds are further compounded not just by the skills you choose, and itemization and other stats that improve those skills, but skill runes that can potentially change their very behavior. And those changes can range from small things like adding a chance to stun, to very extreme things like causing an AoE knockback, and any creatures knocked back repeat that AoE knockback from where they land, and so on and so forth. So there's quite a bit of room for experimentation if not build potential within all of that.
the first part of his posts gives us just one more cookie crumb on how the new skill system is working. He mentions that while the skill tress are still out, the skill tiers are still in. A certain level must still be hit to acquire a certain skill. Only, instead of splitting up the skills into specific types, all the skills are floating around in one giant pool.
Bashiok then continues to talk about avoiding cookie-cutter builds. The idea of every build being equal is impossible. There will always be a particular build of skill choices that allow for the most damage. To limit players choices is not a good way to avoid this. For example, if a player chooses one skill, they are not allowed to have another. The whole point of abolishing the skill trees is to allow players to choose any combination of skills. So how then do you avoid cookie-cutter builds. Bashiok's answer is with fun and exciting builds. Blizzard is attempting to make different builds for different tastes. While many may choose the most damaging builds, other players may choose builds that are played a little differently. Perhaps the most damaging is not always the most fun build to play.
Bashiok finished his post talking about balancing issues for the game. Not only are they testing out the thousands of possible class builds but they are also aware of the affects of different item customization and skill runes. While we have not gotten too much information on what type of customization different armor and weapon choices allow, Blizzard is testing different stat augmentations with the numerous amounts of builds. Perhaps the biggest and most complicated mechanic added to the balancing troubles are the skill runes. Bashiok commented on the range of these effects from adding a small stun to adding a chained combo stun, AoE, and knock back addition to a skill. With so many different systems all affecting balancing for the game, one can only wish to be one of Blizzard's employees who get to play the game for endless amounts of hours testing the game.