There have been a couple of them when VR was a bigger thing but, now that we have wireless VR It's probably not selling all too well.

@Cyberspirit The wireless VR adapters introduce a bit of lag, while for the vast majority of people (including me) it will be the better option.

But I wouldn't consider the backpacks dead yet, just niche.

@CUDAcores89 Backpack used overheat!

Backpack's special attack harshly fell!

http://m.hardocp.com/article/2017/06/15/msi_vr_one_wireless_backpack_review

didn't find a real teardown but a good many reviews