Slack to Stop Storing Historical Content for Free Workspaces

For anyone who would like to extract all their historical data from a free workspace, it turns out you can do that without subscribing. You only get public channels (but you can make private channels public temporarily and set them back again afterward) and files are only linked, not downloaded, which is a loss, but you will get all the text in JSON format.

So here’s a question: What’s a good process/format for making this data human-readable?