Tip #1: "Everyone moves to melee together. The Paladin casts Beacon of Light on himself."
Basically when it's time for everyone to be next to each other, everyone and their mother better move to the melee. If not, they're going to become deceased and that's pretty much the show. The Paladin will use Beacon of Light on himself here to help heal the group.
Tip #2: "When you get the emote for Lightning Nova, everyone moves back together."
I've found this is the tricky part in the fight. When everyone need to move in there is a defined point that they're going to. It's not really relative. "Move to gigantic Tauren DPS Warrior," is easy to understand for everyone. "Move back a few paces," gets to be a little more difficult. Especially if some people's idea of moving back is slowly turning with the keyboard and walking (not running) over. But that's part of the fun of this fight, you have to move together.
Tip #3: Lightning Nova doesn't have a huge range.
This tip made me raise an eyebrow and think for a minute. Lightning Nova really doesn't have a huge range. I'm used to running way the heck out of the nova just for safety's sake, but given that it really doesn't have a large range movement isn't too necessary in the extreme end. Just a little bit of it will do the trick. Well, maybe more than just a little bit, but you get the picture. You don't need to run to left field to get out of the blast.
Tip #4: "You don't need to run all the way back to Loken."
One of the secrets of good tanks is that it is often advantageous to allow the mob to come back to you after having to move. Of course this will necessitate that the DPS slow down or letup entirely as to not pass the tank in threat, but the potential benefits of doing this far outweigh the push in DPS. By allowing the mob to come to you you're essentially resetting the playing field, and in many aspects the encounter. The boss fight simply becomes a rinse-and-repeat exercise. This principle applies to many bosses, no matter if they're difficult 5-man ones like Loken or road blocks like the old Sunwell boss Felmyst. The principal is easy: "Okay, we've done this once we can do it four more times."
Tip #5: "Only spread out slightly."
While Lightning Nova is the worst of Loken's abilities you can't just ignore the others. Since you don't want Arc Lightning to stack up too much you want to be sure to stay spread out a little bit but not too much. You still want to move as a group when you have to, but don't spread out so far that the Paladin (or any other healer) can't hit you with their heals. Everyone staying within 20 to 25 yards of the healer is a good idea.
Tip #6: Loken is about movement and coordination, not about healing.
This is important to realize. If the fight was just about healing or DPS there'd be less movement required (we assume). But it's not. Much of the damage of the fight can be negated by proper movement and coordination of the group. Thus this point is perhaps the most important of them all in that many folks simply want to brute force the encounter. While brute forcing can generally work, especially if you out-gear the environment you're fighting in, it won't work in all situations. Blizzard has evolved their fights over the years and in such an evolution of encounters brute forcing becomes less and less of an option. Each fight requires some sort of gimmick or skill beyond just the typical tank-and-spank. In this case it's moving as a group.
It should be noted that it's relatively rare for a developer to comment on a specific strategy as Ghostcrawler has done. It's not uncommon for them to post about certain abilities in regards to specific kinds of fights, but an all out "here's one way I've seen this boss be killed" isn't something we're used to in WoW.
It could be that this boss is causing so much trouble for a specific class combination that the developers/Blizzard felt the need to comment. Or it could just be part of a discussion about why Paladins are still great healers. We should take caution at reading too much into why Ghostcrawler spoke out about Loken and not another P.I.T.A. mob like Malygos or 3-drake Sartharion.
Nonetheless it's fun to discuss some specific boss strategies for a relatively hard encounter, especially when the developers weigh in on the situation.
Even though these tips came out of a Holy Paladin thread on the official forums, it should be obvious that they can apply to anyone. Replace Bacon of Light with Chain Heal and you have yourself a good Restoration Shaman strategy. Or Circle of Healing, or whatever other AoE healing spell is your choice. Hell, go ahead and Holy Nova is you're uber enough.
The main point still stands – the encounter is not impossible for one class. It's very doable. And as such, it shouldn't really matter what classes you take to heal your group. You might need to adapt and change strategy a bit, but that's just part of the game.