I'm split on removing Immortal from the meta for Ulduar. If they had removed it from Naxx, everyone with Twilight Vanquisher would have a 310% speed proto-drake. They might be the best things this side of whatever, but 310% speed mounts are supposed to be rare and difficult to get. The meta achievement needs to include some barrier, just not an Immortal style achievement that's more annoying than difficult, and that doesn't bar you from hard modes week after week trying to complete it.

Will be an achievement in itself to convince most others to do 'Immortal' in Ulduar if all they get is 10 achievement points, especially when all bosses now got hard modes.
Would be disappointed if thats the solution they go for. Some people clearly don't like to do achievements (especially not if they are going to get less loot because of it), so making raid dependent achievements which require exactly this = bad idea. Just like it was for the undermanning achievements.

I'd rather see a 3-4 'very difficult' achievements in the meta, to replace Immortal.
Both some which requires lots of gearing up (timed kills should be good for that obviously), and some which require good planning and/or skill.
If they really want some Immortal type achievement, it could be for the last few bosses only, while doing hard mode at the same time or similar.

The challenge in doing Immortal is fine enough as such, and I can understand Blizz wanting it in.
However its separating those who want to do achievements and those who 'just' want to raid, more than it should, especially if 'Immortal' is taken out of the meta achievement.

The 310% mount wont even be that big of a carrot for people to do those achi's in Ulduar, as most raiders able to complete them all, are likely to have completed the current one already.

I would pray immortal not be part of the meta purely for the "normal mode drake raid" vs "heroic loot raid" reason that has been mentioned.

In fact I hope, though rather in vein i'd imagine, it gets removed from the Naxx meta too. It wouldn't impact the 10-man meta rareness as it completion rate according to Wowjutsu (i know it's not fully accurate) is 8.7% compared to 3-drakes at 2.9% and 6-min maly at 2.3%. It would also have very little impact on the 25-man rareity since 6-min maly has only a 1.4% completion.

What it's removal would do is mean the reward (the drakes) would be determined by the successful completion of hard fights such as 3drakes, 6-min maly, and not reliant on an achievement which has a degree of randomness in it's aquisition and thus can be unfair.

Strongly hinted above, now explicitly stated:

World of Warcraft - English (NA) Forums -> Realm First Ulduar Clear Achievement

To get a badass title which even fewer people will have than the current Immortal? I'm guessing people will still want to do it.

In response to the person who said it would be good to have a raid achievement which required planning/time, perhaps it would be a good idea to have an achievement which would require differant gear sets from some/all players (Ie resist gear), as aposed to making the achievement just about the abillity to perform certain tasks, this requires people to plan, and build towards it outside of raiding.

Having Immortal runs is interesting and fun when everyone has a ping below 100.

My guild has been trying immortal for almost one month and we have been random deaths on it and majority is due to lag spike or disconnection in popular disconnection fights like thaddius / gluth and 4 horseman. Some may say replace them but saying is easier done then actually puting action into it when my guild consist almost more then 1/4 from malaysia nearly 3/4 of the guilds from singapore.

I really hope this sort of achievement could be scrap away from 3.1 especially to those who are playing at about 400 - 800 ping everyday in raids. Anyway the ping isn't the issue but the disconnection is the worst and the most frustrating among all.

And give up better quality of loot for a week? I'd be truly disappointed with the hard modes if doing them didn't severely hamper your ability to do an immortal run. Likewise, I'm disappointed at an achievement that asks you to give up loot. I don't know why they don't change these achievements to make them personal. Say, kill every Ulduar boss in one raid lockout on hard mode, without dying.

The new Immortal/Undying achievements on PTR have the same title as the Naxx versions.

I think having a full timed run being the "crowning achievement" like immortal is now would be an excellent idea. This is something that RNG is not really gonna be able to screw with very much. If one person DCs it might add a few seconds to a boss kill, but it won't automatically ruin your achievement for the week. It also serves to limit the accessibility, much like immortal, by only being able to be attempted once per week. A really tightly timed speed run is actually fun to attempt instead of just being aggravating.

An 1:45 naxx run for example is fast enough that only very organized raids with good players who stay focused the whole time would be able to pull it off. It also serves to make trash an interesting part of the instance. It would no longer be something that half the raid afks through while the other half put forth minimal effort. Anything that makes trash less boring and mindless seems like a good idea to me. Trash that used to be boring and trivial isn't so boring and trivial when you don't get any time between pulls and have to kill each pack as efficiently as you can.

It would also alleviate the tension caused by failing immortal always resting on a single persons shoulders. Instead, like Jagiya said, it would bring a guild together in supporting one another while trying to get everything done as fast as they can. No longer would it feel like everybody in the raid is pissed at the person who DCed or pulled agro. Instead you would have people being resed asap to help keep the raid moving and tanks and healers working closely together to keep pulls rolling safely.

I doubt it. It will separate those who want achievement points and other flavor like titles even more from those who just want to clear the instance and get their loot.
Do we really need to end with achievement guilds and raid guilds as separate entities. Maybe thats exaggerating the problem a bit, but considering how much annoyance many people have had with just doing the undermmaning achievements in Naxx, this seems to further point in that direction.

Achievements should be out of the ordinary, and represent a challenge, but not go so directly against the other aspects of raiding, like doing Hard modes, or getting loot (which we probably cant deny matters much for many raiders).