Some feedback from the quick 10 we put together last night:
1) I will say that we were going through a learning curve on this fight so the damage profile that I experienced may not stay the same next time around when people better learn how to avoid the incoming that can be avoided. We were also ranged heavy dps which may have some effect.
2) We started working this with 2 tanks (DK, Paladin), 2 Healers (Paladin, Druid) and 6 DPS (5 ranged, 1 melee). We weren't really going for an optimal setup, we just grabbed 10 to check it out. On the first couple pulls, we were a bit surprised by the incoming (at least I was) -- especially the 2 worms but even from the Magnataur. I finally asked if it had an enrage timer and found that it didn't so we had our boomkin swtich to secondary talent resto and things went a TON smoother. At least until everyone starts figuring this out, 3 healer setup would be advised imo. How this translates to 25s, I'm not sure -- maybe 6 healers -- not sure how many tanks we'll need -- 2 may not be sufficient depending on how much impale and his damage get amp'd for 25s.
PHASE 1: On Gormok, Impale will require the tanks to swap after so many applications. Be aware however that, even after it's been taunted off, the other tank will continue taking heavy bleed damage for the next ~30 seconds. You will need to keep rolling heals on them. Incoming on this phase is fairly heavy. I found a good position for this to be in the center (15-20 yds range from Gormok to avoid stomp). This let me reach all ranged DPS that were scattered in a circle around the arena to avoid clumping for fire hits. For 25s, we may want to quadrant heal with tank healers in center and raid healers spanned around with ranged dps. 10 yd split or so is vital due to Fire mechanic. Between Fire and Gormok output, this is where I consistently was rolling the most hps -- things gradually ease up. You may use your innervate at the end of this phase (remember 3 mins now and half mana bar) so that it's up again later. Maybe this will be easier when folks get better at avoiding fire, tanks get taunt rotations down better, etc. but this is what I experienced yesterday.
PHASE 2: Once we got positioning down and learned to manage the worms, this wasn't too bad. Burning Bile and Paralytic Toxin don't do that significant damage and we were healing through Paralytic Toxin at least as frequently as people were running to someone with Burning Bile to clear it. It may make sense to just DPS and heal through it -- maybe not. We kept spread out -- if we do decide to clear Toxin instead of heal through it, it may make sense to stay a bit tighter to shorten distance to run to someone with Burning Bile. We killed Gormok every time and actually died to this phase 2 times before we sorted it out. The two wipes we took to these guys were due to bad positioning, worms not getting picked up after going underground and people getting 3-shot in the span of .6 seconds, key folks being out of range on heals, etc. We also didn't swap our boomkin to resto until after the second death to these guys and that definitely helped phase 1 mana retention and healing in this phase.
In terms of dps split and enrage after one dies -- we dps'd both of these guys simultaneously -- we thought about putting melee on one and ranged on the other but, as mentioned, we were ranged heavy so we just split dps and tracked health. We did this really well one time (died within 5 seconds of each other) and not so well the other time (closer to 30 seconds from one another). Enrage didn't seem that bad though on the 30 sec apart one so maybe you could dps one first then the other if desired.
PHASE 3: You get past the first two phases and this one is crazy simple (at least from healing output perspective). As long as people keep a decent spread and don't get caught in Arctic Breath en masse, raid incoming damage is fairly light. This may have been because we were a ranged heavy comp and your experience may differ if you are melee heavy. After the knockback, it's pretty easy to throw some rejuvs on people and actually have some time to DPS Icehowl during the stun. As a note, if you are DPSing him during the stun (or just standing around regenning), do so at a diaganol. When the stun is over he will flip 180 and frost breath. Also, if you are the one he targets for his charge, strafe the heck to the right or left as soon as you have the ability to move or it's game over. We actually did die to him once but that was because, while I had seen videos, I didn't understand that charge mechanic. I went splat and he enraged (so dead healer plus enraged boss didn't end well). Second attempt -- after I clearly demonstrated to everyone what not to do

-- was easy peasy.
I might be missing something but that's generally it. I'm linking the WWS below for those that want to look at it. It's hardly textbook but, as mentioned, were still figuring everything out. Also, I use Nourish a ton more in 10s than as opposed to 25s where it gets used very minimally.
World of Logs - Real Time Raid Analysis
Separate topic, but probably worth noting -- the deaths to XT Hard Mode later in the parse were due to that fight's mechanic changing. Bomb bots etc were spawning heavy despite placement to one side. This may be bugged, it may be intended, but it's something you might be dealing with next time you see him so be aware.