Mastodon

That's more or less the point of the post though. The affordances framework can be applied retrospectively as well as in the design phase. And software grows and evolves over time, so there is the possibility of divergence from the original design, and that could include intentionally heading towards a different affordance set..

Mastodon doesn't have a complete feature set, and I don't think it aims to be a direct clone of twitter (otherwise there wouldn't have been such resistance to retweets). Seems like the perfect opportunity to think about the problem, while it's still growing.

An alternative is to not bother, and just rely on forking to produce software with different affordances. I think that's a perfectly fine strategy. But there's still value in laying out the mission/values and intended affordances, so someone doesn't fork for a feature that would easily fit within mainline Mastodon's mission (of course, merging a fork is possible, but it can be a PITA).