I think for any app developer, something like this is inevitable to create for someting akin to a social media where user interaction is used.
That being said, I don’t see how this needs to become a core part of Blockstack(.js). This is something implemented by the developer, not by the library, and thus should probably be regulated to a tutorial or FAQ.
As for implementing shared app data (as advertised in SOLID), this has been discussed before but without work being done so far on these “cross-app data buckets,” though I know Stealthy has been working on having cross-app reads/writes via multi-app authentication.
On a side note, it could be possible to use a SOLID Pod as a Gaia Storage backend (i.e. use blockstack sign-in for one pod folder, for all blockstack apps).