Alliance between Kurzick and Luxon would be possible because of the story line in Faction. {side note: 1 alliance can not benefit from the other alliance(s) faction pool}
Now, I'm not sure how alliance will play out in future chapters, but if chapter 3 is any indication, it really doesn't matter.
Now you might say, isn't one alliance big enough? For some, maybe or maybe not. I mean, I've heard of guilds branching off from the alliance to create their own alliance. And the lead guilds would say they are our sister alliance ... yes/no?
There are guilds in my alliance since day 1, and we all became good friends. So, instead of them merging in with another guild within the alliance, because their guild may not be doing well. Maybe it would be better to add another alliance. More guilds=more people=more resources=more fun=more pain?

Thoughts?