MSC3904: Room version 10 as the default room version (#3904)

* Initial Commit for Room version 10 as default

* fix filename

* Give file and filename its MSC number

* Add update progress information

* Update 3904-room-version-10-as-a-default.md

Author: FSG-Cat

proposals/3904-room-version-10-as-a-default.md

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+# MSC3904: Room version 10 as a default
+
+Enough time has passed to allow the public federation to upgrade their servers to support room
+version 10, though with some caveats (see "potential issues"). This proposal aims to make v10 the
+default room version.
+
+## Proposal
+
+The specification adopts v10 as the suggested default room version, making no changes to the stability
+of any room versions. As of writing, v9 is currently the suggested room version.
+
+Room version 10 is currently published here: https://spec.matrix.org/v1.4/rooms/v10/
+
+## Potential issues
+
+Servers will be encouraged to update their config/internal defaults to use v10 instead of v9. This
+is considered a good problem to have.
+
+Note that servers are not required to honour the default room version due to it being a suggestion
+in the specification, however they might fall behind as other servers set their defaults accordingly.
+
+Some server implementations, like Synapse, support configurable default room versions: servers which
+have set this flag will not necessarily be affected by this change.
+
+As of writing (2022-10-09) Synapse and Dendrite both have supported Room version 10 since 2022-08-02
+when Synapse in 1.64.0 added its support. Dendrite added its support back in 2022-06-01. This leaves
+Conduit as the only major implementation to lack v10 support. 
+
+Conduit status for v10 is not implemented as of (2022-10-09) but has been reported that its getting close
+by Conduit developer Timo. Ruma has it implemented and the Catalyst Conduit fork has v10 working 
+for about as long as Synapse has had its implementation based on the memory of the Author of this MSC.
+
+For completeness, some links:
+
+**Conduit**:
+
+* Tracking issue: N/A
+* Library support: https://github.com/ruma/ruma/pull/1213
+* Release: v0.5.0
+* Testing: N/A
+* Update Progress Source: https://gitlab.com/famedly/conduit/-/merge_requests/444/diffs?commit_id=1e1a144dfa98429ef9f02d16045796b73013830d
+
+## Alternatives
+
+None relevant.
+
+## Security considerations
+
+None relevant.
+
+## Unstable prefix
+
+None relevant - servers can already choose a different default room version legally. This MSC
+just formalizes v10 as the default.