Probably never. The complexity is borne by Amazon. Even before any of the development begins if you want a RAID setup with some sort of decent availability you'

Probably never. The complexity is borne by Amazon. Even before any of the development begins if you want a RAID setup with some sort of decent availability you've already multiplied your server costs by the number of replicas you'd need. It's a Sisyphean task that also has little value for most people. Much like twitter it's conceptually simple but it's a hard problem to solve at any scale beyond a toy.