People keep talking about "progression" as if it still existed. Seriously? Wrath progression?
For those who remember (and those who don't), "progression" was a term applied to raiding when progress through a given raid instance was a matter of weeks or months, not hours and amphetamines. "Progression" involved building faction to be PERMITTED to see the later bosses and farming all necessary gear from the bosses you could down in order to make killing the later ones possible.
If you're going to be directly impacted by the release delays then be THANKFUL that Blizz is giving you a longer period of time in ICC before you're groaning and grumbling through a boss fight. Hell, this is one of the reasons I'm avoiding the PTR's: content burnout has been a persistent problem in Wrath raiding.
Last, it's been said, bears repeating: This is Arthas, the most lore-rich boss we've yet had the opportunity to face. Seriously, would anyone NOT be a little let down if he dropped within 48 hours of the patch? World-first Shadowmourne within 72?