Per my comment above I have a prototype of this feature up at https://github.com/chiaracoetzee/fluxer-subprofiles/tree/features/subprofiles based on @haileyscommit's design and it's working well on our home server. It's web/desktop client only not mobile right now. Would need a lot more prep before submitting a proper PR. Supports both GUI subprofile selection and PluralKit-style prefixes, and can import a system from a PluralKit JSON export dump. Tested with a large imported system with 60+ members. Some screenshots below for reference.
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We decided for now to settle on the "Personas" language (because it's widely-understood and to avoid the issue where "subprofiles" may be confused with server profiles). This isn't the most popular term in the plural community (they prefer "identities") but I think it's clearer to a general audience and we can emphasize in the messaging that this isn't just for fictional roleplay.
Also decided to forego the "proxy" term which only really made sense in the historical PluralKit context which proxied messages through a bot. So instead of "proxy tag" we use "persona tag" or just "tag", and instead of "autoproxy" we use "Active Persona Mode".
Can revisit terminology as needed.
Also did a bunch of style fix-ups, using proper Fluxer Button components, avoiding Discord CSS tags and colors, gave "Last Used" a nowrap, tested in light theme. And haileyscommit did the feature above to show succinctly who a persona belongs to on each message, as well as supporting deep links to persona settings, a slash command for latch control, and a visibility toggle for the persona composer adornment.
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