(I ask this
because today we have a lot of interest in append-only logs, like in
Dat, Secure Scuttlebutt, and of course blockchains—systems where
information cannot be repudiated after it's published. If Wikipedia
rejects append-only logs and allows official history to be changed,
per this hypothesis, then that's a really weighty argument against
those systems.)

Wikipedia does allow history to be changed, but this has caused lots of problems with the Analytics pipelines.  It's the main reason you can't get fresh data in the same way you get it for pageviews, even though pageview data is 3 orders of magnitude bigger.  So I wouldn't follow Wikipedia's example too closely here :)