Why has video not taken up it's mantle?
Possibly because it's too unreliable. Still.
I use video chat on skype and QQ on my home broadband connection, and even across the world it seems to work fine.
I would list several reasons why (and it's not the end point application like Naptard says it is)
1. Incompatible products - everyone has a phone and single identifiable phone number. If I want to voice call my friends and family, I just call their number. I have about 25% of my contact book on Skype. The others, only their phone number. Either they don't have Skype, or I just can't be bothered to get their Skype address. So for every new app that is released that can do video, there's a separate contact list to keep.
As an example, Skype is terrible on phones. It never stays logged in, or it takes up too much memory that garbage collection comes around and kills it off if I open 1 or 2 new apps. This happens on Android and my iPad under iOS. So I'm never online long enough for people to call me. THEREFORE I can't just pick up my phone and dial like I would a phone number. Everyone has to be online at the right time.
Apple may have made an attempt with facetime to integrate it a little - but there is a REASON why they made it Wi-Fi only (however restricting that is). The current networks are just not good enough, as are the methods of actually initiating the call.
If there was some way to start a video chat simply by dialling the telephone number and choosing voice or video - I think a whole bunch more people would go for it. It would become second nature. I think 3 in the UK tried this for a while - do they still do it? But again, the problem is here - VENDOR LOCK-IN. Apple, 3 - only if you mates are on the same network or device, can you make easy, established ways to make video calls.
So we've got some key limiting factors: time, place, device, accessibility.
2. Video chews through bandwidth. Had the telcos kept the unlimited usage wonderlands, we might have finally got around to make video a part of our everyday business, but right now, they just don't want you / I / us using video all the time. They haven't turned on enough of their dormant capacity / aren't through charging exorbitant rates yet to welcome wholesale use of video
3. Video is time sensitive to delivery of packets. Voice is too if over an IP network, but it's a connected network and the established infrastructure is there to handle it. True, voice will also cut off in a tunnel, but the 3G / HSPA services are just not realiable enough, on the move, to give us satisfactory video chats. Skype suffers immeasurably over a wi-fi network for good quality video. It's different to standard video streaming with all the processing that needs to be done either side.
4. Devices aren't good enough. The cameras that go into phones - especially the front ones, go in as an after thought. They're ostensibly put there for the very subject of this article, for video chat. But nobody ever uses them - because they're not integrated as natural addition to the telephone network.
Until every phone network goes IP and Data only and even voice is across the data streams, so we can connect video to our phone numbers, then we won't take to the all seeing-all dancing video future. When this happens, over the top apps (Talk, Skype, et al) won't be needed, because the video call will be second nature. Pick up my phone, press the picture of my wife on the screen and a few seconds later it's replaced by a real-life grinning version of her.
Moreover on top of this - I've seen plenty of articles suggesting that telcos are worried about becoming simply commodity players, only providing the tubes for the dominating companies (Google, Facebook et al). Well, if they got their act together and actually started moving towards integrating the video into the network like this, without the need for apps or other providers, they could have a bonafide reason to start offering package deals and making money off of it, like they did with SMSs. Once again, 3 already did it. Why not the rest?
I for one, would welcome our new video overlords. Although I don't really fancy sitting on my metro to work in China listening to all the locals getting their face-time in with their squeeze early in the morning.. They're already loud enough on the phone - I fear with video the din would be deafening.