I don't think it needs to be "mainstream" even in the upcoming gen, in the way that phones/laptops are "mainstream".

For the initial market I think that replacing work/gaming PCs is a good enough start. I'd love to be able to fully replace my gaming PC/work computer with something like this. (And I'm keeping a close eye on simula VR. ;) )

Batteries imo is the biggest hurdle, something this intense with only a two hour battery life like other portable devices, steam deck, is a real issue to being a drop in replacement for a work laptop.

EDIT: Also as far as a killer app, I don't think video calls are the right way to look at it per se.

Immediate and immersive personal connection are a huge plus imo. Example, would you rather see your long distance parter on a phone screen, or in full body form sitting next to you?