My bet is still on a break-through in write-once storage, which wouldn't just be useful for life logging but could also work wonders with a storage system like Datomic (with persistent/purely functional data structures.)
I read an interesting paper in Science about backing up data to DNA as a future archive scenario. At the time I hadn't realized you could just store DNA by drying it out and putting it on an index card, I had visions of cryo vats of test tubes :-). Such a system would be a 'write once' sort of solution.