Document the model behind implementation traction

proposals/spec-lifecycle-implementation-traction.md

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+# Describing Implementation Traction
+
+Capturing and representing the likelihood of traction for a given specification by would-be implementors require adapting to the specific implementation ecosystem the specification targets.
+
+This proposal currently focuses only on the browser ecosystem as it is the most instrumented to capture the various nuances of interest from implementers. We expect to provide (likely simpler) mechanisms to capture similar information from other ecosystems.
+
+## Browser implementer ecosystem
+
+To capture the full range of intentions in the browser ecosystem, we suggest distinguishing:
+* browser distributors, e.g. Google, Microsoft, Mozilla, Apple,…
+* browser implementers - the same, but also organizations known to contribute to browser implementation, e.g. Igalia, Intel,…
+* shipping browsers - user-facing product, e.g. Chrome, Edge, Firefox, Safari, …
+* browser codebases, which for simplicity we suggest designating by the underlying rendering engine: Chromium, Gecko, WebKit, …
+
+We think the following signals can be attributed to these types of entities to inform how much traction a specification has or is likely to gain. These are ordered from the least significative to the most:
+* browser implementers making substantive contributions to the spec
+* browser distributors or browser codebase publishing their "standards position" about the spec - at this stage, Mozilla (an implementer) and WebKit (a codebase) publish standard positions
+* browser codebases being updated with an implementation of the spec
+* browser distributor distributing the said implementation in a restricted fashion (behind a flag, through an origin trial)
+* browser distributors distributing the said implementation without restrictions
+
+Given existing research about which compatibility data developers use to make decisions about whether or not to adopt a web feature, we propose to start by documenting information matching the [WebDX Community Group core browser set](https://web-platform-dx.github.io/web-features/#how-do-features-become-part-of-baseline%3F), while also supporting documentation of additional browsers, codebases, distributors and implementers.