You mean when she's not on the train too? That's not going to happen anytime soon, because mobile networks are far too crappy. On public transport in a major city in germany I regularly get latencies of 60+ seconds (yes, seconds) and a bandwidth of a few kilobytes/s max. There are also spots where you don't get any connection at all or you get a connection but it's so congested that you can't even make a DNS request that doesn't time out. Yes, I'm still talking about the middle of a big city. That's on the Eplus/O2 network.
Other than the added privacy, I'm having trouble imagining the advantages of that. I'm reading my facebook feed, but now nobody else can see it, oh boy!
But see, I already don't care if people see. So that doesn't help me. Being immersed might actually hurt me though. Honestly, the idea of being on a train and having no idea what's going on around me is kind of terrifying.
Zuck knows he failed with Facebook Home. He has surveyed the landscape and he knows he'll never be more than the most-used app on someone else's phone. But he's still salivating to own a platform, so he's looking to the future.
Think about this: if you're sitting on the train, or waiting in the Doctor's office, would you rather wait in VR, or in a waiting room with your nose in a mobile phone?
And if you remove all of the bored killing-time-in-spaces-you'd-rather-not-be uses of mobile phones, how much use is really left in them?
Think too, how many phone calls will you make when you can run around a virtual dinosaur park, or sit under a virtual night sky with your friends and family?
I don't know the answer to these questions, but it does seem like VR could put quite a lot of pressure on what is now the dominant category of computing devices. And Zuck is better positioned than anyone to be the pack leader.
Also consider that phones are fundamentally disconnected from remote friends. You don't really want your sister scrolling through the news with you when you're on the train. But you might be totally happy to have her sitting next to you in a flowery meadow in VR while you both catch up on your news feed. Or maybe she is on the surface of Mars and you are in a flowery meadow but you both feel like you are together. Maybe she's fighting aliens in a forest while you are collecting mushrooms, bantering back and forth about what happened at work.
VR is fundamentally more amenable to social than flat screens are. Look no further than social console gaming to see the start of this. I think the merger of Facebook and Oculus is fascinating.