I would like to be able to use multiple accounts simultaneously with the option of viewing individual timeslines or an “everything” timeline. On the Everything timeline, the UI would indicate which account is showing (and therefore commenting) that particular post.

For reference take a look at the Liftoff! app - it adds a "via " next to the communtiy name *eg !fediverse@lemmy.world via sh.itjustworks *- indicating fediverse community on lemmy.world instance coming from my sh.itjust.works account.

Purpose - for accounts on defederated instances, or on instances with communities being blocked on some other instances