I'm eventually foreseeing a whole new form of cache. A coil of optical fiber with the cache data constantly inflight around that loop. With denser optical data transmissions the amount of data per meter of coil starts increasing.

At this speed, we are already talking 2% of the entire Internet traffic in the length of a single fiber between the shortest point between the UK and USA. That's just a single fiber. As transducers of this ability get cheaper and cheaper, all those unused dark fibers start to offer up alternative uses with inflight-caches. Think of how much memory would be needed to store that amount of data, how much that costs and even with the costs of fiber, things would start.