If the 150 hours of burn in is so critical to the final sound product, why didn't they burn them in to the 150 hour mark before they boxed and shipped them? Audio gd does that with many of their products.
Is the 24 ohm rating part of the problem? From reading through this thread and some of the reviews, it appears that getting the amp/ Nighthawk synergy right is essential to getting the most out of them. I was surprised when my Hawks liked the hybrid Ember better than another hybrid and a solid state.
The cost in the labor and additional equipment it would take to burn in headphones, say, 150 hours would have to get tacked on to the price the consumer pays for them. If nothing else, not burning them in in the factory makes them more affordable to produce and to purchase. Couple that with the fact that, to put it mildly, there is some disagreement about the effects of burn-in, that means that not everyone would be willing to pay for that part of the production process. There would be a perceived increase in value for some potential customers, no increase for others, and a decrease in perceived value for others. Plus, there isn't a really solid consensus on
how burn-in should be done. People disagree about volume, duration, pink noise versus brown noise, and all kinds of details. The safest bet then is to leave the burn-in to the customers, to do it as they see fit.
The 24 ohm nominal impedance won't create any problems, per se, you will just have to be careful about what amplifier you pair it with. For example, the Topping DX7s has an output impedance of 10 ohm on single-ended and 20 ohm on balanced. Pairing the Hawks with that amp would mean a very unideal damping factor that will skew the resulting frequency response of the headphones. But, that's it. That's worst case scenario. It certainly won't break them and, hell, you might even prefer the sound. If you want to play it safe, try to pair these with an amp with a low output impedance, around 1 ohm or lower, and you won't have to worry about it.
...There will be a few trolls along the way but it is interesting reading.
That should be the Head-Fi motto...