If "For the Alliance" was gonna resonate, it already would have.
"For the Horde" and "Lok'tar Ogar" capture the excitement and imagination and even, of all things, the inner RP-er of players on Horde-side. In the rare event on Thrall that the Alliance win WG, you'll see a small army of people by the raid portal in Dalaran waiting to go in and take it back, popping wings, Divine Storm (pre-4.0.1
), battle shouts, etc and /yelling "For the Horde" and "Lok'tar Ogar", and I'll tell ya that it's pretty rare that the offensive battle *doesn't* get the time achievement.
Some of this comes from questing, IMO -- just in "Lich King", the induction of the Taunka in the Horde has that awesome oath. The Wrathgate cinematic (genuinely inspirational for both factions, IMO) has that awesome moment of Saurfang leading his Horde into the battle with the call-and-response (FOR THE HORDE! you can hear his troops answer back).
The potential is there for Alliance -- I'm a Horde player, but I'm pretty impartial, I think people sound ridiculous when they are like "ugh, I'd never play Alliance/Horde". On the PTR for 3.3 I made an Alliance toon specifically to do the questing and Alliance version of the Wrathgate, and was genuinely inspired by how Bolvar gets involved in the questing and you can see what's there to psyche up Alliance players and, also, why it's so poignant to lose Bolvar at the Wrathgate. Prior to that, my Alliance experience has been levelling a Paladin up to the mid-30s (before I had an 80, any heirlooms, or they were cross faction, so I did it "for real" with no bags, no money, no twink stuff, etc -- took a while since it was all alt play), and I was able to kind of get into the majesty of Stormwind and so on, and I remember distinctly a cool quest where Jaina shows up outside Theramore to save your butt.
But through all of that, I never once had an iconic image of what being in the Alliance actually meant to the character, so why would it transfer to me as a player? "For the Alliance" or "Light bless you" or "King's honor, friend" are all read by the voice actors as just sort of casual greetings. Compare to a Horde orc NPC saying "For the Horde!" -- he's pumped and all he's gonna do is sell you some cheese.
What they need to come up with is a phrase that stands on its own and would connect to the passion of the NPCs/characters, because without that, the players never pick up on it. And to do that, it needs to be integrated from the time you first get your class trainer letter, etc.
I'm not really sure what it could be. I was just skimming through the "An End and a Beginning" quest on wowwiki and all of Bolvar's dialogue... "Honor, Courage, Compassion, and Justice!"... "Be free and join the victory!"... there's potential in some of these things, but they'd have to be distilled into one simple, repeatable, iconic thought.
I think the key is brainstorming what the Alliance
is -- what is it for, what do those in it have that they didn't before, what unifies them? Hordeside, that's easy; the Horde of old and new both revel in shared power and purpose and victory as ends unto themselves, very Klingon. For the races that join them, it's about shared survival in that power, purpose, and victory.
So what defines the Alliance? Answer that question and the catchphrase will write itself for you.