What I still dont get from this post is if the data stored and timestamped can be "big".
For example, if I wanted to store 10000 sessions per second, would it even be possible via the blockchain hash? For the sake of the conversation, lets say these are orders on a very large web store, and I want to store the price + time of the order of an item.
In your terminology, yes, the data can be "big". As "big" as you want. From your example, I think you'd be interested in what Factom are doing - http://factom.org/.
From a quick glance I cant gather if they utilize sending a Bitcoin dust payment to an address or not. Do you know? If they do, it wouldn be good as the dust can quickly run into billions.
EDIT: Nevermind, they use a local merkle tree and gather multiple values in one batch and hash that. I guess we either get sidechains or we keep getting these "solutions" to data storage.