the way extensibility works in a closed-world #fediverse is that "every implementer talks to every other implementer". or maybe there is a central registry of extensions that everyone submits to their authority, as stewards of the "protocol" that is used to build the "network". this trades out the n:n relation between implementers and other implementers, for an n:1 relation between implementers and the central registry.
the way extensibility works in an open-world #Web is you just do it.
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the challenge in closed-world systems is how to scale communication and coordination as the number of implementers grows. without a central authority, it almost inevitably leads to power coalescing in the hands of the few most popular or largest implementations, who become the "de facto" standard and get to mostly do what they want, and everyone else mostly has to follow if they want to be compatible.
sound familiar? it should, because this is the model that the #fediverse follows today.
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