https://www.mediawiki.org/wiki/Technical_Collaboration_Guidance/Community_decisions mentions the goodness of early feedback and early adoption of new features, as a well as hints about a mechanism by which communities could request to be part of first release waves when they are excited about a feature.
However, there are no hints about how this works in practice. How do communities know that new features will be available for communities willing to try them out? How they can officially declare themselves interested? Milestone communication doesn't provide any details either.
Many potential solutions are possible, but for the sake of recommending good practices it would be useful to offer one by default. Looking at the current situation and our discussions, it seems that most of those solutions go through Tech Ambassadors, a role that we are thinking of refining and promoting.