I understand why he did it, but, the end result just wasn't particularly appealing. There's no real/actual benefit here. Now, if he was able to charge AND use a headphone at the same time, then he's added something. But, there are Y cables available right now that are able to do just that.
I admire his tenacity and his creativity, but, it's just not that amazing.. He's ruined the water proofing and/or the barometer for the ability to not have a dongle attached to his favorite pair of headphones. Or, you know, just use Bluetooth.
There is benefit to him, obviously. Not everyone has the same needs or use case. I think you're still missing the point of the video, it is not to say "you should do this or I did it because I had to"... he did it because he wanted to see if it COULD be done, that's it. Yes you can use this or that, yes he ruined the water resistance (there is no waterproofing here). Who cares though? It's his device .. it's not yours, it's not mine. The video was neat from a technical point of view.