Alter to reserve v7 instead of declare v7

proposals/2998-rooms-v7.md

@@ -1,14 +1,26 @@
-# MSCXXXX: Room Version 7
+# MSC2998: Room Version 7
 
 A new room version, `7`, is proposed using [room version 6](https://matrix.org/docs/spec/rooms/v6.html) as a base
 and incorporating the following MSCs:
 
-* [MSC2176](https://github.com/matrix-org/matrix-doc/pull/2176) - Update the redaction rules.
 * [MSC2403](https://github.com/matrix-org/matrix-doc/pull/2403) - Add "knock" feature.
 
-
 Though other MSCs are capable of being included in this version, they do not have sufficient implementation to be
 considered stable enough for v7 rooms. A future room version may still include them.
 
 Room version 7 upon being added to the specification shall be considered stable. No other room versions are affected
-by this MSC.
+by this MSC. Before v7 can enter the specification, MSC2403 needs sufficient review to be eligible to enter the spec
+itself. This MSC is reserving the room version for use in broader testing of MSC2403 - this does not make MSC2403
+stable for use in most implementations.
+
+## A note on spec process
+
+The spec core team has accepted "knocking" as a concept, and is generally aligned on the ideas proposed by MSC2403. As
+such, we're going ahead with reserving a room version number early for some broader testing given MSC2403 is near to the
+point of being stable itself. Typically the team would declare a room version number once all the included MSCs are
+eligible for becoming stable, however in this case it's ideal to push ahead and reserve the version number.
+
+If MSC2403 were to be replaced or otherwise be rejected for some reason, we'd ultimately have a gap in room versions
+which might look weird but does not necessarily have an impact on the specification: room versions have no associative
+ordering, so skipping a perceived sequential version is valid. The sequential versioning is a human ideal, not one of
+the spec.