A New Fate

On one side of Spirit of Master Shang Xi inside the Temple of Five Dawns will stand Delora Lionheart and Aysa Cloudsinger, and the other side will stand Ji Firepaw and Korga Strongmane.

After turning in New Allies, a short scene will occur.

Spirit of Master Shang Xi says: You've all accomplished a great thing in saving Shen-zin Su. You do us all proud.
Spirit of Master Shang Xi says: It seems your journeys are not done. These new allies of ours come from a broken world that could use our help.
Aysa Cloudsinger says: Master Shang Xi, I would like to accompany the Alliance back to their home.
Spirit of Master Shang Xi says: What of you, Ji? Will you join the Horde in their journey back?
Ji Firepaw says: Yes... perhaps that is for the best. I like what I've seen of them, and it sounds as though their world would use my help.
Spirit of Master Shang Xi says: And you, my young student? Where will you go?

You can talk to Aysa, Delora and Ji before you decide as well.

If you talk to Aysa Sloudsinger, she says the following:

I understand that the mind of the Tushui is not the only path to wisdom, but there are yet choices that should not be accepted. Risks that are too dangerous to ever be taken. Decisions that I cannot forgive...

It is time for me to leave Shen-zin Su. I have found respect for Delora Lionheart for her confidence and valor, and her people. I do not yet know if I will find a home there, but wherever my path may lead, I will find a way to help the world beyond this isle.

Despite everything, I've enjoyed what little time we've had together, <Name>. I hope that you may join me, but I understand that this decision is not an easy one.

If you talk to Delora Lionheart, she will say the following:

You are our first turn of good fortune in several days. We're glad to have the help.

On the other hand, Ji Firepaw says this:

This day seems to be one full of hard decisions. Having the courage to make them is gravely important, for the sake of us all. I did what I had to do, and we may have all been doomed if I had not... but sadly, not all see it that way.

It is time for me to leave Shen-zin Su, that those here might be free from the burden of my difficult choice, and that I might fight on for the sake of a much larger world.

I've only known Korga for a short time, but he and I could be brothers if he were born in a different skin - he possesses bravery and honor that I would gladly stand beside. You too could be my brother/sister, after all we've gone through together. I'm hoping you might join us, but I understand that there is much to consider.

Korga Strongmane doesn't even have anything to say which was rather interesting. Maybe Blizzard forgot to put one in, or he's just a "strong, silent type" kind of person.

To make your decision, just talk to Spirit of Master Shang Xi. He will say this:

There's a broken world that could use your help, my student. Have you decided who you would like to accompany in your journey?

I'm ready to decide.

If you click on I'm ready to decide, a pop-up will show up with a brief description for each faction and two very important buttons: Join the Alliance and Join the Horde. If you decide to join the Alliance, you will become Alliance along with Aysa Cloudsinger and Jojo Ironbrew. If you decide to join the Horde, Ji Firepaw will accompany you. You can change factions anytime but it would require you to buy a Faction Change from the Blizzard site, so make your choice wisely. You can back out of the screen by simply pressing ESC if you're not sure or you want to explore the island - once you've made your decision, you will never come back!

If anyone is curious, here's a brief description for each faction:

The Alliance
The noble races of the Alliance are bound together by proud traditions of nobility, honor, faith, justice and sacrifice.

The many different Alliance peoples all contribute their technical, arcane, and spiritual wisdom toward the goal of a peaceful and just world.

Take up their banner to represent the high ideals of the Alliance throughout Azeroth and beyond.

For the Alliance!

The Horde
The proud nations of the Horde are loosely joined in an alliance of convenience against a hostile world that would see them destroyed.

Focused, ferocious and sometimes monstrous, the Horde values strength and honor, but struggles to keep aggression in check.

Join the Horde and fight to build a world where their people can live free.

For the Horde!

Without picking a faction, you can...
...wear any heirlooms you've collected.
...level to level cap via herbalism and/or mining.
...learn and level any primary professions to level 75. [npc=65043] and [npc=57620] are the trainers.
...learn how to make up to 28 glyphs via inscription using herbs collected on the island.
...learn how to make an additional 21 glyphs via inscription using mageroyal, which can be obtained with herbalism from [npc=55640].
...have access to any of the 4 forges or 4 anvils on the island.
...stow your pet with the 1 stable master so that you can tame more pets as a hunter. [npc=68986]
...summon vanity pets from either faction.
...not ride any mount except Sea Turtle.
...not participate in player versus player activities.
...not participate in pet battles.
...not make nor join a guild.
...not have access to a mailbox.
...not learn any secondary professions, due to a lack of secondary profession trainers.
...not change your spec once you pick one nor duel spec, due to the lack of class trainers.
...not change your talents nor glyphs once you pick them, due to a lack of class trainers and access to items that can remove talents and glyphs.
...not leave the island by any known means, this includes zen pilgrimage, mage teleports, glyphed astral recall, death location exploits, dungeon/battleground queues, graveyard exploits, and outside assistance from players in another faction, as all these means have been either hotfixed to not work or never worked to begin with.

Click the choose option in the quest text. You will see a brief description of both Alliance and Horde with "Join the Alliance" and "Join the Horde" buttons below said descriptions. Think it over if you need to and then; Choose your destiny! (faction), Horde or Alliance...