Just a little run-down of possible (not confirmed) clan-based advantages/disadvantages:
Crab: +1/+1 against the Shadowlands
Crane: Double Attacks during surprise rounds
Dragon: -25% to artifact construction costs
Fox: +20% to spying and resisting scrying
Lion: +1 PL per territory per turn (minimum IR of 1 required)
Mantis: +1/+1 during Naval Battles
Nezumi: Immune to taint, +0/+1 against Shadowlands
Phoenix: -25% to epic spell costs
Scorpion: +20% to diplomatic subversion and spying
Unicorn: Can take a +5/-5 for 1 round each turn
Shadowlands: 10% chance to subvert defeated enemies
Bloodspeakers: +20% to diplomatic subversion and -10% to costs for creating an epic level spell
Why are these my current picks?
Crab: Duh, it's about half of many crabs life... I was also considering an advantage to fortresses or something, but I dropped it in favor of just this.
Crane: They are the masters of dueling, and are still quite courtly... I was stuck between giving NPCs advantages, and giving diplomatic subversion advantages. I dropped both when I thought of the Iaijutsu skill that allows two cuts in one strike. That sort of inspired me to give them two attacks if they ever successfully surprise someone.
Dragon: I half chose this because of Avarial's style of play he is hinting at, and I half chose it because dragons=treasure=artifacts... Both of which show a relation to this.
Fox: I'm not sure what Kal's style is, but at first I was thinking of adding PL from the plane of animals each turn. Or an advantage while fighting in that plane. Later I considered that fox's hide in dens, and yet they are still quite agile hunters. They can hide well, and they hunt well... hmmm... that's how I came up with my answer.
Lion: I was thinking immunity to fear, and similar things. Then I thoght about it, and changed it to focusing on the once huge Lion armies. Of course, it also reflects some of Serpenteyes style of play from the last IR.
Mantis: I like the Mantis Clan having the strongest Navy. I also was thinking of the mantis in a rougish light. I finally decided to lean towards the navy in the end.
Nezumi: Since no faction is all-nezumi, I thought the advantage shouldn't be too powerful. I made them quite good at what they do, but not infinitely good at it. I focused on racial traits, but then again just immunity was kind of lame, so I added the bonus in as well.
Pheonix: Well... magic. That's the only thought I had on this matter. I also considered some of the feats and stuff, but magic is the whole primary factor.
Unicorn: I was stuck here at first, then I decided to focus on the rage instead of the horse/unicorn thing. The Rage type affect will probably end a fight in one round, however it only works once per turn. This is obviously the most combat-strong ability, so it had to have the drawbacks I listed. Basically with a -5 defense you have no chance of blocking while you rage.
Shadowlands: We discussed 5% before, but I decided they need more punch than that. 10% sounds slightly more reasonable, so I took it up. They also are immune to taint, but it's not really a special ability.
Bloodspeakers: Aimed for the ability to create epic spells (though normally not the nice kind) almost as good as the pheonix clan, but they also get that diplomatic subversion bonus, which if played right could steal a characters NPC deck.
Ahh, thanks 
