Exciting on so many levels.
First: it is practical and doable now, while having the saving-the-world vibes. I thoroughly support this idea. I think the advances in storage will soon enough (sooner than AIs reach the rewriting-history stage) allow us to record multiple physical copies of the 100+Tb database and spread them out throughout our habitat, making the revisionist AIs’ task significantly more difficult.
An even grander idea: laser-beam the data into space, aiming at several stars at different distances, and listen to the echoes coming back, reflected from the star system’s components. These echoes will be super weak but hopefully detectable and decipherable with future technology, and importantly, it will be absolutely unforgeable by AIs here on earth. For example, aim at a star 50ly away and get back your data in 100 years, guaranteed untampered.
But then, I think that your list of “what it takes for this to work” misses a critical item:
7. Those in the future who care about knowing the truth will need the guts to accept that data about the past contained in these hashed torrents is true, even if it contradicts their ideas and memories of that past.
I think that for superintelligent AIs it will be much easier to convince us all (and probably themselves) in a wrong version of the past, perhaps combined with faking some evidence, than seek and subvert all the evidence there is. I find it quite probable that this is the road they will take first, and they won’t even much care about subverting your hashed torrents because it won’t be necessary.
Imagine you live in a future. Imagine you are as confident of your memories and your general idea of the past as you are now. Imagine you get interested, verify the hashes and timestamps, unzip the torrents, start to read, and start seeing references about pink unicorns everywhere! Imagine all these papers and books mention pink unicorns as a pretty common thing that exists, and can be seen, experienced, studied, filmed, etc.
What do you think would be a more common outcome then:
You decide that your whole idea of what existed in the past is wrong, and you relearn it all from scratch from those zipped torrents, incorporating pink unicorns into it.
You decide this is someone’s elaborate hoax, post it online for lulz, and go on with your life undisturbed.
I think I would prefer a future in which AIs do all the non-teacher work and leave humans teach each other, so that ~50% of workforce is teachers and we no longer have the bottleneck and mass-production problems in education. Reason for my preference: I think in such a world, a human-only referendum on “are we in dystopia?” has more chances to be defeated.