While I have no doubt that there is evidence of all kinds of fun crimes hanging out in the Steem blockchain, I don't think it's likely that Steemit Inc. or other major stakeholders expected HF 21 to be of any use in dealing with that fact. Mainly because to get rid of the evidence would be to get rid of the blockchain and there are way too many copies of it floating around for that to be very effective.

Radical transparency is one of the few things that this place has going for it and I don't really see anything in HF 21 that was intended to actually change the historical data that way.

Now, if one of the new developments as a way to essentially "checkpoint" the blockchain, consolidate all the old blocks into some new kind of "checkpoint" blocks which stand as computational cipher and capitalizations and allow the chain of blocks to be rolled back to that point and still checksum, then I think you might have a strong argument that some folks in the blockchain were trying to get rid of information they didn't want seen. As it stands, since that is not a technical possibility, suggesting it is a bit of a stretch.

It would make for an amusing conspiracy theory but not really a failure of the kind that we normally see playing out here.