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I like that version of the Katana the best.  It matches the high crit feature of our western curved blade and is simpler than changing two things on the one-handed use.

Samurai as a title not a build or class.  Yeah I see what everyone is saying.  I think that's best.  Applying the Katana to a background seems like a good idea but those only add a +2 to Skills.  Not sure it's a fair/balanced option.  I suppose still making chars buy the Superior weapon feat would work.  If they want to play a Samurai then the feat could represent a cost to gain their noble heritage.  It also represents the additional training they have.  It's still a choice to the player to build a char around the katana or another weapon.

Schools

Crab = Fighter
Crane = ?
Dragon = Tempest or TWF Ranger
Lion = Warlord
Phoenix = ?
Scorpion = ?
Unicorn = Warlord Archer or Ranger Archer

Not sure how to cover some of the more dexterous schools.  Could you build a Samurai from a rogue?
I'd like to have an option for the Iaijutsu concept.  Any thoughts for early level stuff or build this into a paragon?

The clans are clans of Samurai that like to embody some form of fighthing style, I thought... It's been a long while since I've read 3e OA. Or at least have some type of traditional something or another.

Look at... Wind Rise Ports background feature, I mean the background can do a little more than just +2 to skills. But, it would be alright to have the Feat as an investment to being a "real" samurai in the setting. The other swords are just katana shaped longswords. Or something. Which I think is fitting.

I also don't remember what Iajutsu does...

Or put back in properly. I wouldn't count out anything that could be an interesting part of what it meant to play OA. I'd have to look at it, and see how it worked and how it could be... given a 4e rendition.

The clans and the styles, I was thinking would be more like weapon multi-class feats, with maybe changes to how you wielded a katana...

Take for and idea, the Musashi Tempest Style or something:
The first feat would allow the prof with a Katana, and maybe using it one handed withouth losing the extra proficiency bonus. Then the next feat would allow Tempest Strike, and so forth.

Or if a Clan really favored the Spear, somehow or another you can wield a two handed spear in one hand and the Katana in another. The entire point would be make it that if you actually took clan feats or style feats you would be a more distinct samurai. Well at least, that how I think it would be.

That's why it could be a weapon feat. Or those weapon multi-class feats.

I've been a little curious on this one, too. Here's my two cents:

Samurai depends on build. There's tempest and great weapon fighter as possibilities, as well as taclord and archerlord. Archerlord is great since many samurai were archers, anyway.

Ninja...well, I could shamelessly plug my ninja class, but truthfully, this also depends on build. If you want martial ninja, rogue is perfect. Take the Alchemist feat and you can make all their tools of the trade (smoke bombs, poisons, etc.) Mystical ninja would be good as assassins.

Sohei always sounded like a cleric or monk, most likely monk.

Shugenja sounds more like a wizard or maybe a sorcerer. Sorcerer appears more feasible as I never pegged shugenja for bookworms, but of course, everything's relative.

Wu jen make me think druids, what with their communion with spirits and deriving their power from nature.

As for iaijutsu, you could tie that to the Bluff skill. Specifically, the feint to gain combat advantage. You could make a feat that could let you draw a weapon and "feint" as a minor action, keying the check off Strength instead of Charisma. You could peg on 1d6 + Strength mod extra damage if the check works (and you hit the next attack you make against the enemy that turn), but I wouldn't scale that damage. Straight extra damage from feats (such as Brutal Accuracy) don't scale, but you'll make your point