Video was also the feature that was going to justify the 3G spectrum auction prices. In the UK many billions were paid by the telcos and part of the marketing promise at the time was the then 'obvious' application of video calling. We would all be chatting by video on our flip phones, not sending txt messages. txt messages were an accidental phenomenon as I understand it, something squeezed into the chatter needed for the phone to stay in touch with base station.
Cameras in phones by Nokia et al. from 2005 are with this in mind, front facing, VGA video that is handled at the phone level as a video call:
https://en.wikipedia.org/wiki/Nokia_N70
There is no 'app' that puts the video in a http stream somehow, this was baked in functionality, now abandoned by telcos.
Yet there is the selfie phenomenon, again something that few imagined to be the thing it is. Cameras used to point outwards, now they point at the owner. I would not be surprised if cheap phones only come with selfie cameras soon, much like how laptops only come with 'selfie cameras'.
A large tablet for just doing Facebook and Facebook video does not sound portable enough for what it does, 'phablets' are better on the commute, why carry another device? Sounds to me as if Facebook are trying to hard on all the failed VR apps.