I’m really not sold here on adding this to the FEP when all of this is specified in the ActivityPub specification - people just don’t use it when it comes to C2S. Managing collections is a core part of the spec.
I guess I see an argument for specifying that emoji catalogs should be a “well known” collection provided by the server, but isn’t that the standard for collections? User-created collections aren’t specified in the ActivityPub spec.