As part of some discussions with Jim Maddock (see his recent thread https://lists.wikimedia.org/hyperkitty/list/wiki-research-l@lists.wikimedia.org/thread/INT2D2XGJ4YO2NVYBNKOOQMVI6OXKG32/), I started a meta page to catalog some of the many natural experiments https://en.wikipedia.org/wiki/Natural_experiment that impact the Wikimedia projects. I've seeded it with some examples (censorship, Wikipedia Zero, lockdowns, Public Domain Day, new data centers, etc.) but am certain that there are many more out there. If folks on this list know of other examples, please edit the page below boldly or respond on thread and I'll migrate examples onto the page.

https://meta.wikimedia.org/wiki/Research:Natural_experiments

Best, Isaac