e.g. I write a short summary for Twitter, slightly longer for mstdn, longer still for FB and full length for medium or a markdown readme. If I have media, include where possible.. incl primary screenshot/social preview selection, or multi-screenshot. Or video. Email support++
I see the value mainly as a time save, but also quality checker eg for staging w/previews, so the simplest version of this could be a static page that just help prepare the content.
It gets me thinking about managing/remembering logins, aggregating stats and responding to comments, etc.. I suppose CORS would kill this for the more proprietary channels. Should be APIs for the good ones.
And throw some AI in for good measure: during composition, let me start with what I have and fill out drafts for the rest. For responding to comments, maybe autosuggest short responses for common FAQs, or help me build FAQs as I go.
Sorry, don't mean to hijack.. haven't seen this being handled well.