Provide context and remove hunt for more useless fields

proposals/3989-redact-origin-field.md

@@ -1,16 +1,29 @@
 # MSC3989: Redact `origin` field on events
 
 The [current redaction algorithm](https://spec.matrix.org/v1.6/rooms/v10/#redactions) *keeps* the
-top-level `origin` field on events during redaction, however the only use of it as of writing is
-a malformed example of event format. The field has no significant meaning in modern room versions.
-
-Note: some other fields are additionally useless in modern room versions, however they are already
-adapted by [MSC2176](https://github.com/matrix-org/matrix-spec-proposals/pull/2176).
-
-This proposal's scope includes *removing* other fields which are useless in modern room versions,
-however makes no effort or consideration for *adding* protected fields to the redaction algorithm.
-Given MSC2176, the only useless field appears to be `origin`, however the author kindly asks that
-reviewers point out other examples as they arise.
+top-level `origin` field on events during redaction, however the only use of it within the spec
+as of writing is a malformed example of event format. The field has no significant meaning in
+modern room versions.
+
+Within the ecosystem, it's clear that we'd [prefer the field to disappear](https://github.com/matrix-org/matrix-spec/issues/374),
+and have [tried to do so](https://github.com/matrix-org/matrix-spec/pull/998) in the past. The
+malformed examples are even [known to us](https://github.com/matrix-org/matrix-spec/issues/1480).
+
+What's not clear, and mentioned in [a comment](https://github.com/matrix-org/matrix-spec/issues/1480#issuecomment-1495183789),
+is whether the `origin` field is *acutally* used. There do not appear to be any auth rules or similar
+which would use the field, however it'd hardly be the first time that the spec was wrong about an
+ancient room version like v1. What is clear is that Synapse, where this question would be asked,
+wants to [drop support](https://github.com/matrix-org/synapse/issues/3816) for the field and has
+taken [steps](https://github.com/matrix-org/synapse/pull/8324) towards that mission by fixing bugs
+in the area. In a [quick audit](https://github.com/matrix-org/matrix-spec-proposals/pull/3989#issuecomment-1497659507)
+of the Synapse codebase during implementation of this MSC, the `origin` field appears unused.
+
+Given the above context, this proposal removes the `origin` field from the redaction algorithm in
+future room versions, leaving it as-is for existing versions (not that an MSC can change the behaviour
+of an already-stable room version).
+
+Some other fields are additionally useless in modern room versions, however they are already adapted
+by [MSC2176](https://github.com/matrix-org/matrix-spec-proposals/pull/2176).
 
 ## Proposal