There was a good post by @mav a few weeks back about data storage stats. One interesting fact was that most data is stored, immediately read, then only accessed infrequently afterwards. For this sort of data, robust write-once storage options seem almost ideal.
I suspect an ideal setup would have hot copies of new data stored to solid state, prior being replaced with long term cold storage solutions. Essentially, a cache for these long term, cheaper, storage mediums. The cache can then be freed up to be used for new data, which would expect some subsequent read access.
Given that we have appendable data types, SAFENetwork seems to fit this model well. Subsequent changes would be stored on hot, fast access media, with related data being pulled from cold storage to hot storage too.
I suspect the economics of such an architecture would encourage its adoption, as storing rarely accessed data on expensive, fast media would seem uneconomical.
@mav link here: Object storage prior art and lit review