Aanyway, I don't want to rehash the whole conversation, but I do want to comment on Sou's
Now I don't know about you, but I've never tried to hold a phone or Skype conversation with more than about 15 people at a time, twenty max I think. I've attended lots of teleconferences and web-based discussions lately, and with almost all of them there have been communications difficulties. Even today one cannot be confident that simple telephony will work for everyone for a couple of hours. Most of the electronic meetings involving 10 to 15 people have suffered with static/hiss, drop-outs, difficulties with web-documents and so forth. To hold a conversation with upwards of 30 people is quite a challenge, let alone gatherings of hundreds or thousands or tens of thousands of people.This is classic "perfect substitution threshold" stuff: we won't accept your new way of doing things, unless it does all the old things, and better. But why would you want to do this? The current way of holding conferences - correct me if the world has evolved in the ten years since I left Science - is that a pile of people turn up in a place and so you have to work out what to do with this pile of people, and the obvious thing is to dump them in a lecture theatre and have them be lectured at. There are usually poster sessions, coffee breaks, breakout sessions and so on; but conferences are usually built around the armature of lectures.
And yet time after time people report that the most productive part of conferences is meeting and talking to individuals. Sometimes because you've been sparked by something in their lecture, sometimes by some other chance or design. The idea, in this day and age, that you need to go to a conference to read someone's presentation is absurd; they are all online, or could be, far more conveniently.
And so if you were going to re-invent conferences online, there's no reason why you'd want to replicate the current format, or anything close to it. There are various obstacles in the way of Nirvana, of course. The linked articles note that going to lots of conferences is one marker of status. Not mentioned - but the reason that I mostly went - is that it is of course fun to go to foreign places with someone else paying. There's also the huge academic inertia of the current conference circuit.
1. Probably chez ATTP, though I didn't join the conversation.
* How much would we have to adjust our lifestyle to stop global warming?
*  Yes, I Get on Planes to Fight Climate Change - Alex Steffen. "People will always find excuses to do what they wanted to do anyway".