It seems to me the main reason people don't go for such a Blockchain is because they don't 'trust' Amazon. Fair enough - why not then have a blockchain owned by several different competing companies with huge data centers: Google, Amazon, IBM etc. This solves the computation and scalability issue with blockchain while also making it less likely one company gets too powerful (any new transaction will need to be confirmed by all the parties (Amazon, Google) providing a self regulating mechanism).