#XMPP has specified a base set of features, beyond what's in the core protocol, for properly serving a number of different use cases in 2019; core, web, IM, mobile:
This is a good sign that the network might finally be ready to evolve beyond 1990s style #Jabber IM.
I'm not aware of anyone who sees "feature inconsistency" as a feature. The actual feature is extensibility and the cost is inconsistency.
The compliance suites are an attempt to "fix" this as much as is possible in a distributed, anarchical community.
The XSF is working on adding compliance badges so that projects can advertise their level of conformance.
Things however happen slowly because the FOSS XMPP community is small and largely made up of volunteers.
I guess that's the best possible argument for feature inconsistency but I doubt it's worth it.
IMO you can get biodiversity by having multiple independent implementations in different languages and platforms while still implementing the same spec and being largely mutually compatible and feature consistent.
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