Where has it seriously been tried other than the remote only sprint I organised? (which I think worked ok).
The problem I have seen is that the remote sprinting has not been taken seriously. It needs to be treated as a first class citizen and not an after thought. Often the only form of remote collaboration at a sprint is live stream of intro and end of day demos, often with really bad audio so its hard to hear. IRC doesn;t work because what is happening locally is audio.
Alternatively you could make it mandatory that every team has a hangout, and everyone screenshares and has audio on all the time. Or some similar system that tries to get close to the a) being involved in conversations b) being able to discuss code without explicitly setting up a new call.
The 2nd problem with online sprints is commitment. When someone has paid to go to a place and their family, friends, other commitments are on hold, they have 100% attendance (normally). This is harder to solve. One way to potentially solve is that remote sprinters pay to attend, and perhaps get their money back at the end if they did attend 90% of the time? Maybe there are other ways or rewarding full attendance?
3rd question is why go to all that hassle? Hopefully the answer should be obvious. Not everyone is in europe. Not everyone has the means to attend. But there is the desire and some do have the time.