Chosen nickname/alias of a user should be respected (imported) when inviting them to a new space/room

[heyakyra]

Suggestion

This is a hopefully more useful evolution of the concept of pet-names for chats element-hq/element-meta#725 (overriding real room/user names with custom display names #188) by combining two in-progress ideas.

1. Support per-room display-names Support for per-room display names/avatars element-hq/element-meta#499 (API for changing display name in a space/room API for changing displayname in a specific room (SPEC-230) #103)
2. Canonical DMs / 1:1 chats MSC2199: Canonical DMs matrix-spec-proposals#2199 (element Introduction of a simplified room for conventional 1:1 messaging element-hq/element-meta#1467 synapse Support for Canonical DMs element-hq/synapse#6261)

If a user were to send a /myroomnick ALIAS command to a canonical DM, the other user in the room could automatically import that alias into any new spaces/channels when inviting the aliased-user. This would mean when inviting a user to any space/community, there would be a quick check against the canonical 1-on-1 chat for a preferred alias, then if one exists it would be copied into the room/space.

Note: It might be worth considering the privacy implications of this (maybe the user should accept the invitation and the alias separately?) similar to existing leaks of nicknames across homeservers matrix-org/synapse#5677

Related:

• Decouple human-readable aliases from MXIDs: We need to re-consider splitting users into alias & underlying opaque ID (SPEC-152) #63 (per-space/room profiles MSC3189: Per-room/per-space profiles matrix-spec-proposals#3189 remove MXIDs from events [WIP] MSC1228: Removing MXIDs from events matrix-spec-proposals#1228)
• Decentralized accounts Decentralised user accounts #246 and identity Decentralised identity (SPEC-458) #203
• Rename users Rename user element-hq/synapse#12174 forward MXID Implement ID forwarding (like email .forward files) (SPEC-156) #65 and transfer space/channel memberships Ability to transfer channel membership between homeservers #238