For people with serious medical conditions that need to communicate that to EMS, we have physical medalert bracelets that can tell healthcare providers that you have diabetes or epelipsy. That technology works even if your provider doesn't have power or reliable internet.
Most patient provider interactions don't require history transmission because you're at a scheduled office visit or your in emergency care at a facility that is part of your giant local health network. In those cases, providers can look up your name (that they can get from your wallet even if you're not conscious) in their database and find all they need. They don't have to worry about synchronizing data with arbitrary providers and trying to remap their ontologies or deal with lossy translations.
The number of cases where providers need fine grained history information for people that they've never treated before and they need it right NOW and can't afford to wait is...very small relative to the volume of patients treated. I mean, if you've been shot in the chest, the ER is going to focus on keeping you from bleeding to death rather than poring through a history to note that you're allergic to ragweed pollen, have slightly elevated blood pressure and fractured your tibia 8 years ago.
Beyond that, a medical history that can't be updated is pretty useless, but our fragmented healthcare system isn't able to agree on standards for electronic medical records or how to synchronize them across different providers. Actually, getting doctors to use EMRs will probably be the work of a generation.
Then the problem becomes, how do you get doctors and hospitals to use something like this? Creating a private database that providers could optionally use seems doable. The hard part would be creating a large enough percentage of adoption at first. After that, more and more providers would see the benefit of using the system, and patients might even start asking for it, or preferring hospitals that have it.
Reluctance to change, for two. You have to convince most hospitals to change from whatever they have installed now to your system, or you have to make your system 100% compatible with the current hospital systems, with minimal changes.
+ People don't know how good it would be until it's actually used, so adaption would be slow.
+ No real financial gain- health providers just add the cost of bureaucracy into the bill.
So yes, it would be cool/useful, but there's not exactly a huge need for it (and many potential problems).
This is a much much better way round, but two things hold it back - well three.
1. Key sign? PKi? Wtf?
2. Doctors actually don't want many records to be available to the patient - it frankly compromises medical care (heard the phrase GOMER - Get Out Of My ER. Much diagnosis is still hunch and guesswork - and needs to be carefully phrased If patient will read it
3. We still think something centralised should track all our medical care when really something decentralised is much much better
I can't remember any of the others, but all of the predictions for around now (other then the smartphone one) are completely and totally off. All of these prediction things are bullshit, as most futurist ideas generally are. There's no accountability, because no one will remember the reports. It's ridiculous that the government pays people to write these things, and just as ridiculous that Wired publishes them.
I think SMBC put it best:
http://www.smbc-comics.com/?db=comics&id=1968#comic