It is something I've seen quite frequently, although not usually using full-sized cans.
Still, an interesting feature. I found it intriguing when I saw the picture and couldn't make up my mind - good to have but maybe use or never use? Gimmick? (Which I want to be *really clear* - unlike the blog press, gimmick is a good word to me. I don't find gimmicks something to look down upon. I like gimmicks - they indicate design thought. Bluetooth started out as a gimmick, along with NFC, fingerprint sensors and a slew of other goodies.)
So just from a marketing angle alone, I think that the dual headphones are already working. I may forget Marshall, I may forget Marshall London, but I'll never forget "two headphone Android" and Google is my friend - so by extension, that gimmick has made the name stick. Even if I need Google to help later.
WifelyMon and I have used cans together with a splitter with individual volume controls - our noise-cancelling Sonys that we'll use on airplanes or trains sometimes. Not an audiophile application but not foreign to me personally.
Had the picture shown two sets of earbuds instead of cans, for just me personally, none of the above would have kicked in - I'd have been *meh* all over it.
The Marshall comes with earbuds AFAICT. And will probably what most will be using.
Can't and won't argue that - higher popularity, convenience, and generally price (although high end earbuds exist).
But in the same adding-to-that spirit as my earlier post, I want to share something that was a pleasant and very intriguing epiphany for me.
Background - back in the day, I owned Stax electret and electrostatic headphones. They ran off the speaker outputs of a very beefy 150 W/channel amp. Very niche back in the day, not many had them, I eventually sold mine and thought they'd died out.
But - just like Mangepans or electrostatic speakers, they were outstanding because they were planar rather than point sources.
http://www.innerfidelity.com/content/how-planar-magnetic-headphones-work
Fast forward to last year and this - I helped with the One M8 HK mods (if you don't know me, stop and do not be impressed - I'm not bragging and I only helped with the installer and minor stuff) - and from that, I got to chat with a LOT of people getting that mod on the regular M8.
And what I learned was interesting.
First, planar headphones are very much alive and well.
Second - a LOT of HTC One M8 HK mod users were using planar headphones that eclipsed the cost of the phone, from $1000 on up - the Audeze being popular -
http://www.headphone.com/collections/planar-magnetic-headphones
I finally got some in Hangouts and was able to ask, as someone who understands planars, why they were spending a thousand or better for phone cans.
It turned out to be a stupid question with a simple answer -
Audiophiles either already own planar headphones (or whatever they consider to be the best) or are on their way to getting them for all private listening, regardless.
They weren't getting the headsets to match the phone - they were upgrading the phone to match the headsets.
So I think that the Marshall will help sell some better earbuds.
But it's not going to help sell good cans.
Good cans are going to help sell the phone.
Hope this makes sense.