Blizzard loves 10-person content guilds just as much as we love 25-person content guilds. The reason for having this mount in the 25-person Lich King encounter has to do with maintaining the proper distribution of such awesomeness. If it were available in the 10-person encounter as well, it may become too prolific and lose some of its initial unique qualities.
Will there be a 10-man version of Invicible?
There are other plans in motion on that front and we are not at liberty to discuss them yet.
Lich King fight – 10 vs 25
As for whether or not we are concerned about the possibility of 25-person geared players heading in to the 10-person Heroic and potentially trivializing the encounter… Yes, of course we are. Can we make a fight that has absolutely nothing to do with gear? Yes we can, but that would be counter to the growth of the characters involved. Gear influences every style of gameplay(Tank/Damage/Healing) in some way or another. To make it entirely divorced from the Lich King encounter wouldn’t be the most epic experience we could deliver. There will be a massive skill portion to this encounter, but we are not going to move gear 100% out of the equation.
There are unfortunate side effects of maintaining two distinct types of raids. The raid with the smaller number of people participating has to be tuned around that style of participation, made for the people who have been a part of that group. Whereas the raid with the greater number of players is likewise geared toward that larger group. The more people you have, the more difficult (numerically) you can make the encounters. This also means that you can factor in certain amounts of leeway in larger groups and tighten those. I.E. There will be more healers, thus there can be more raid damage; there will be more tanks, thus there can be more encounters that benefit from additional tank mechanics and so forth.
Now, all that is just to say, the Lich King encounter versions given to the two groups are tuned to each individual 10 or 25 person type. The tweaking we are able to do, on the larger group version, can be pulled even further toward the very top end of super hard. While the 10 person encounter must continue to rely only on items achievable and composition available to players in the that raid type. This lends itself to players from the 25-person raid seeking out achievements and other bonuses in 10-player content, but we cannot tune around their excursion into this area without also excluding the very crowd that this content was intended for. That does not mean that it will be trivially easy for one group to move in either direction, but that is intended to be the case. We want the Lich King to be difficult, in-both 10 and 25 versions and we hope that you all enjoy this climactic encounter.