Mirumoto schools
Why can't you learn their Kenjutsu skill? If they use Ken for Iaj, wouldn't you then learn whatever they're using instead of the most skilled master's form showing up as zero skill ranks?

You can’t learn it because that isn’t one of the things listed as one of the things you can learn. This has been confirmed as not a oversight by both Shawn and Rich.

It is because ze mirumoto are sneaky like ze ninja!

There is no functional difference between the Kenjutsu styles taught by the different Clans and Families, including the Mirumoto. Being able to swap Kenjutsu for Iaijutsu has nothing to do with having a special brand of Kenjutsu, it's the result of a Technique. A Shiba Bushi who learned Kenjutsu at a Shiba dojo and has 5 ranks in it, who later joins a Mirumoto dojo and learns the rank 1 Mirumoto Bushi Technique doesn't have to relearn his Kenjutsu ranks to be able to swap them for Iaijutsu: any and all ranks he has, whether he learned them as a Shiba or Mirumoto, are applicable towards the swap. Likewise, a Mirumoto Bushi who Multiple Schools to another School and studies Kenjutsu there can apply any and all ranks he acquires at that other School towards his swapping Technique. The same goes for Iaijutsu. For all intents and purposes, it's one and the same skill for everyone.

I think it's a pretty cool flavor thing that a Mirumoto's dueling style is harder to read than others'. But then, I'm playing a Mirumoto.

I have no problem with it balance wise. It just seems goofy to think about. You step back and view your opponents stance and have NO clue how good he is at dueling even though you're evaluating his stance. It makes duels of stance absolutely worthless to know who's better. -- At any rate, we've always allowed it to be learned in my home game so it's not a huge bother to me. It's just that I disagree with the RAW.

You can still learn their traits, Wound modifier, Void Points...

True. But I, personally, find it silly that I can't tell whether someone has 10 kenjutsu or 1. The more skilled they are, the more it should reflect in their stance. It's sort of the point of the stance. I'm not arguing with the way it's being run or anything in the TOT, just that I disagree with the rule. At any rate it's not a huge issue or anything.

That sounds like a cool homebrew application for Know the School. Learn your opponent's Kenjutsu.

Unless you're up against a Bayushi Courtier. A Bayushi Courtier cannot use a Void Point to lie about their Skills, just about their Traits.

So a Bayushi Courtier 2 wins duels of stance pretty much automatically. Interesting.