Interesting stuff. It makes me think though, the blockchain is a ledger of events, so you can trace a coin (a hash) as it transfers around the place. There is some space with the hash you can put small amounts of data in (like other hashes). People say its a clock, but really its a rolling ledger for these hashes. A bitcoin is a hash (basically) so the data is the hash really, or its a hash with no data if you think that way.
So I see many projects looking at this and great, good to see things being tried. Now I think further, what are we trying to achieve here. Seems like its proof a document exists (a hash of it in the blockchain), so there is somewhere a thing that has this fingerprint. So we need to be able to find the thing (the document) and if its digitally signed and dated (date included in the doc so its signed in) we can validate, yes this is a contract agreed by these two (or more) parties.
Great stuff.
So in SAFE we have immutable data (stuff that cannot be deleted), that is content of files right now. We also have public data, this is data where the data map (key to the files) is unencrypted and therefore readable by anyone. This allows public data to exist, it is signed by an owner (this is the MPID part currently going in to allow public ID’s and messaging etc.)
So this gives us the web if you like, we can publish data and everyone can see it, the data can be in any form we wish, html, .doc, pdf etc. and that is cool. We can do safe::david/web/ to get to my web site etc. fine and dandy.
However I can delete this data (I signed the directory element (this holds data maps for all files in a directory)). So like the web you can delete your own site etc. All well and good again.
However, with a tiny change here this can provide what I think these systems are looking for and maybe a bit more.
If there was location to store to immutably then this all changes. All we need to do is have a mechanism where the client does not sign the directory listing (meaning it cannot be changed as the network sees this as immutable data) but still uploads it to their public place (safe::david/public_record ) then the only difference is that data and directory are immuable and cannot be changed or deleted (permanent).
Then you can open a document (it can still be encrypted if it is indeed a proof you need to have, but want private) and the network can easily authenticate the digital signature (its inherent in SAFE and happens a lot under the hood anyway, for many reasons) and the content of that document is guaranteed. So if it is a mortgage application then you sign, the bank signs and it’s locked, you can store a copy in your public place and so could the bank. Then the data is immutable, digitally signed and if necessary encrypted (you can store it in your private drive if it is sensitive).
Then you have, proof of existence, proof of content and immutability (so no deleting the evidence or governments loosing data type issues). For public accountability this seems to me very easy.
For private contracts then all you do is not publish it, but keep it for your own records/evidence etc. and Bobs yer uncle as they say 
So I see this as very simple really, when you have a secure autonomous network that has inbuilt cryptographic security. the importance of the hash is fine, but its the ability to get the content I think SAFE provides as when its public and immutable it is forever and if SAFE II comes along all you do is drag the files form SAFE I to that place.
then projects like factom can create apps that track contracts etc. or create their own public drive to store certain data on, genverments can place their data there for public record and more. So for a globally secured public record tracking system then it seems job done, The only cost would be store the data, but if it is public data like that then its either free or the cost of private versions would be so little its immeasurable to humans (a single doc with a few hundred pages I would imagine would be a nanopayment and not noticeable), I think you would need to store thousands of such docs to see a cost really, as there is no transaction costs in safe then this would prove to be incredibly cheap and importantly present the actual data that is permanent record.