I don't agree at all.
For instance, consider email or newsgroups formats, with key-value attribute headers, with the difference of putting them at the bottom of the file.
With each "item" being a text file, you could easily fit the average person's Facebook profile into a zip file of (folder-arranged) text files with the content at the top and the extra attributes (e.g. timestamp, reply-to, etc.) below.
Even for someone very active, this would only be several hundred text files per day, so several hundred thousand per year, and several million for an entire profile. With that many, you'd probably have to split them up, but for the average person with maybe several hundred thousand, that's a manageable number of textfiles to put into a zip file.
These textfiles could be almost trivially imported into a relational database with a simple script.
At the same time, the user can also browse the contents of the zip file if the folder structure is arranged thoughtfully.
Of course, I am talking about text only, not images or videos. For these, you would have to either use metadata or have a matching text-file to go with the file.