@mint @crunklord420 @NonPlayableClown @Saxophone3784 @alex FEP-c390 is implemented in Mitra, along with a migration mechanism based on it (which can work even if the original instance is down). But this migration mechanism only works for followers, and it hasn't been implemented by other projects, so it is not particularly interesting. I consider FEP-c390 deprecated (though it might be useful for other things besides migrations).
FEP-ef61 is much better because it makes all objects portable and self-authenticating. I haven't implemented it fully, it is a work in progress.