While we reported a while back on the use of the Essence of the Immortals as a method to unlock the Sunwell Plateau 25-man, progressive patching has continued its march, as Tigole explains to us in a recent forum thread.
The Essence of the Immortals itself is now gone, and instead, all gates will open automatically over time on each server. Tigole explains that although they like the idea of cross-server competition, and plan to implement in the future, The Essence of the Immortals concept wasn't working out as well as they'd hoped. Of course, servers can still compete to unlock the daily quests the fastest.
There's a few explanations as to why they could have decided against using the essences. The most obvious would be that on low population servers, or servers without a robust raiding population, there might be trouble getting the whole sunwell area unlocked before the release of WoTLK, which is honestly probably a legitimate concern. This will also allow raid groups who are interested in world firsts to compete on a bit more equal footing, without having to worry about whether their server has enough other raids going to help boost them to timely gate openings.
Of course, the other question is why they're leaving in the individual gates, and simply opening them over time. Why not just leave the whole dungeon open to whoever wants to take it? Is it because the gates are an important part of the storyline? Or is it an attempt to "trickle in" content so that raiders can have a steady stream of "new" content until WoTLK comes out?