It's not true to say that many Japanese repro companies cannot create natural indigo jeans - it's just that the market has not called for it since about 2005/2006.
Keep in mind Oni Denim is a trading brand, not a factory/workshop brand, the same workshop & fabrics can be had by other companies should they choose to...Oni's niche in the market allows them to sell this kind of product right now, whilst others have since veered away from natural indigo denims. Sugar Cane & SDA were doing natural indigo from many different regions in Japan before the Shaoi came out, and indeed the natural indigo denim revival in Japan occured in the 1990s...we're just catching the tailwind of a dying trend here (no pun intended.)
Yes, I know about the various models they've come out with - I still own the ultra slubby 18 oz pair from 2009 (which they re-issued this year) and I have that single-stitch construct pair you mentioned.
My point, again, is variety...part & parcel with the niche that Oni occupies in the market.
I'm not talking about fits either, more about the fabric & construct, which is what is most important to their fan-base.
No point in this argument - again, I love Oni Denim, but when it comes down the process of sourcing & manufacturing, it is not so different from some it's peers like SDA, etc - it just happens to be smaller, more specialised, and have a slightly different appeal to a straight-forward reproduction brand.
I wrote up a small rant about Oni Denim and it's connection to the 1st generation Japanese denim brands here: