Ignoring Lore per se; make a faction of your 6 favorite races:

[Grubjuice]

If I could make a faction of my six favorite races it would be:
Orcs, Worgen, Trolls, Gnomes, Pandaren, and Goblins


if one could include non-playable races it would be:
Orcs, Worgen, Satyrs, Naga, Ogres and Trolls

[Deleted]

Orcs, Forsaken, Trolls, Tauren, Goblins, Worgen.

[Zlebar]

Humans, Orcs, Worgen, Blood Elves, Dwarves, Goblins

[Wildberry]

Orcs, Orcs, Orcs, Orcs, Orcs, Orcs.

[Deleted]

Mok'nathal, Ethereals, Orcs, Worgen, undead, mogu

it could work, worgen and undead might not be too happy, but at least they could share gilneas :P and im not sure the mogu would join a faction.

[Joey Ray III]

gnomes, goblins, dwarfs, trolls, orcs, tauren

[Wyrt]

Draenei, trolls, tauren, worgen, blood elves, and dryads.

It could totally work.

[melodramocracy]

Orcs, Blood Elves, Night Elves, Tauren, Vyrkul, Tol'vir

Honorary mention: Saurok.

[Abstieg]

Forsaken, goblins, gnomes, orcs, trolls, tauren, all led by the Banshee Queen to wipe out the rest of the filth. (Blood Elves can keep Quel'thalas and serve as a lesser race to us.)

[Deleted]

Forsaken, Orcs, Tauren, Worgen, Troll, Goblin.

What faction do you think I play?

[Z3ROR]

Orcs, Dwarves, Night Elves, Humans, Goblins, Pygmy's.

[Vvulf]

Basically, horde as it is already, but give us Worgen, and allies get Goblins.

[dryankem]

Gnomes, Dwarfs, Tauren, Pandaren, Trolls, Goblin - Now that would be a party.

[bufferunderrun]

Orcs, Ogres, Yaungol, Vrykul, Dwarves, Worgen, Saurok, Goblins, Forsaken, Quilboar and Troll but only if the berserker and dire troll skin is available

Human, Nelf, Belf, Gnome, Tauren, Taunka, Jinju, Pandaren, Hozen, Tuskarr and Furblog

[Psilo]

Night Elves, Dwarves, Gnomes, Trolls, Goblins, Forsaken, Ethereals

[Deleted]

Murloc, Gorloc, Mur'gul, Deep Sea Murloc, Mutant Murloc and Jinyu

[Benomatic]

alliance dwarves, night elves, humans, horde. ogres trolls, goblins

[Extrakt]

Night Elves, Humans, Draenei, dwarves and High Elves/Blood Elves ( It's just the name )

And perhaps gnomes. Friendly bunch of fellas.

[Grubjuice]

the Confederation of Unaligned Azerothian Beast-Peoples (CUABP):
Tuskar, Furbolg, Wolvar, Saurok, Yaungol, Mantid, Murlocs, Gnolls, Kobolds, Makrura, Virmen, Grummle

[Zuben]

Blood elves, dwarves, Forsaken, orcs, humans, goblins.