MSC3820: Room version 11 (#3820)

* Room version 11 rough cut

* Cut a different set of MSCs

* v10 is specified

proposals/3820-rooms-v11.md

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+# MSC3604: Room Version 11
+
+A new room version, `11`, is proposed using [room version 10](https://spec.matrix.org/v1.7/rooms/v10/) as a base
+and incorporating the following MSCs:
+
+* [MSC2174](https://github.com/matrix-org/matrix-spec-proposals/pull/2174) - Move `redacts` to sane place
+* [MSC2175](https://github.com/matrix-org/matrix-spec-proposals/pull/2175) - Remove `creator` field from `m.room.create` events
+* [MSC2176](https://github.com/matrix-org/matrix-spec-proposals/pull/2176) - Updates to redaction rules
+* [MSC3989](https://github.com/matrix-org/matrix-spec-proposals/pull/3989) - Redact `origin` on events
+* [MSC3821](https://github.com/matrix-org/matrix-spec-proposals/pull/3821) - More updates to redaction rules
+
+Though other MSCs are capable of being included in this version, they do not have sufficient implementation to be
+considered stable enough for v11 rooms. A future room version may still include them. Such examples of ineligible MSCs
+are:
+
+* [MSC2244](https://github.com/matrix-org/matrix-spec-proposals/pull/2244) - Mass redactions
+* A number of MSCs which have not yet been accepted (they are not iterated here).
+
+Room version 11 upon being added to the specification shall be considered stable. No other room versions are affected
+by this MSC.
+
+## Unstable prefix
+
+Implementations looking to test v11 before written into the specification should use `org.matrix.msc3820.opt2`
+as the room version, treating it as unstable.
+
+Note: `org.matrix.msc3820.opt1` is from a prior draft of this proposal, consisting of different MSCs than the
+current iteration. Implementations should not treat opt1 the same as other unstable-for-MSC3820 versions.