No reason to limit the EQ to headphones. The app could drive the EQ of your stereo system.

I'm pretty deaf and wear power digital hearing aids. I would love headphones that have the trim of my aids built in because I can't normally wear headphones over them due to feedback and discomfort. When you say that they sound amazing to "everyone", I have found when it comes to technology for me and the hearing impaired community, that probably doesn't include us but maybe this comment will serve as an impetus for better products and services.

I was very interested to see this article about headphones and how they might be used to aid the hearing impaired. I use headphones to make my hearing aides more efficient when using my cellphone. The hearing aides are blue-toothed to my phone; that alone was a great improvement. But when driving or in any other place with a lot of ambient noise it's still difficult to hear, especially if the other party doesn't have a great connection.
To overcome that problem I bought a pair of simple, noise blocking headphones (non-electronic) - $14.00 at Home Depot. They're a little large and obtrusive - you might be embarased to use them in some public places - but they've improved my ability to use my cell phone 110%. I can drive on the interstate with the windows open and talk in a normal tone on the phone. There are expensive, electronic noise-canceling headphones available that are cosmetically more appealing, but they're anywhere from $150 to $400. Give it a shot. For $14 ya can't go wrong!

The technology behind these headphones is nothing short of amazing! They are certain to be a commercial success; I'll make sure to get mine.
Wouldn't it be great if that technology were someday transferred to hearing aids? I'm sure I can speak for the multitude with hearing loss like I have when I say that today's best hearing aids are both expensive and inadequate. This is probably a much bigger market opportunity than headphones!
Self-tuning hearing aids for under a grand! What a concept! GO, NURA, GO!!

This is interesting. I get that these headphones could produce sound that is more "pleasing" to an individual, but isn't the goal of audio "reproduction" to actually "reproduce" audio reality as closely as possible?
On the one hand, it should not matter what the condition of a user's ears are--they are what they are when exposed to the sonic environment of the world around them. If that environment is reproduced and delivered to the user's ears faithfully, then that is what the user should perceive as the "best quality" sound experience. Sonic accuracy is an objective parameter. The subjective part comes in when, for example, one expresses a preference for the sound of one guitar over another. But once the choice is made, the "ideal" reproduction chain should not affect that chosen guitar sound, however bright or dull it may be.
On the other hand, if the headphones can compensate for hearing loss, or can compensate for some other playback system non-linearities (since the "ideal" condition may be otherwise unattainable), then OK.
Again, I don't want to take away whatever "pleases" the listener, but I question the basic premise of altering sound depending on the physical parameters of healthy ears.

I'm amused about deferring to recording engineers for guidance, as they have some of the most erratic hearing of any group, while often maintaining that they can compensate for it perfectly. They have been listening at too-high levels for years.
I would suggest that the extent of the equalization required by most people is a good deal less than 20dB.
But the feedback approach to characterization is interesting.

@erb2000, you can't use this for speakers. As you move, your position changes relative to your surroundings and the speakers, which changes how things sound. With headphones, the drivers are always in the same position relative to your ears while you're wearing them. It's a consistent sonic cavity, unlike a room you're moving around in.

So basically you have to use them only on smartphones...

Have been listening to STAX headphones for years. They are currently the finest sounding headphones on the market. Please look into their electrostatic earspeaker delivery system, as it's quite different from other headphones. I believe it will blend marvelously with your current designs.
Thanks, Dave

OK. So these headphones give you what you perceive as the perfect sound. How do you set the EQ for your master track? If everybody hears sound differently, then a recording sounds different to each person. A sound engineer cannot use these. He needs a flat response pair of speaker monitors
Surely you set up your EQ curve on your playback equipment to what suits you, as you listen through your own headphones. As I see it , you don't need to spend $300.