More important is actually using the new DM semantics:

When I choose 'start chat' (currently 'invite people') from the plus button: if i only select one person, it should invite them as a DM (i.e. with is_direct true).
Ability to untag a room as a DM
Ability to tag a room as a DM for a given user (see Ability to tag a room as a DM for a given user #748)
DMs are tracked in the account_data.
If there is already a DM for the user, we should reuse it when hitting 'start chat'.
If there are multiple DMs for the user, we should prompt which ones to reuse when hitting 'start chat' (see If there are multiple DMs for the user, we should prompt which ones to reuse when hitting 'start chat' #749)
'Start chat' in the Member Details page should instead list the rooms you have in common with the user, as per vector-web.
When inviting someone into an existing room, it should be tagged as DM or not depending on the intent for the room. (see https://github.com/matrix-org/matrix-react-sdk/blob/master/src/Rooms.js#L64 for heuristic mechanism).
Ensure 1:1 rooms are created with equal ops on both sides (the trusted_private_chat preset)

Converting existing rooms to/from DMs #715

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