Even if an object implements AtkStreamableContent, the StreamableContent implementaiton code, cspi wrappers, and other bits have bugs that make the resulting interface nonfunctional.  This was only recently discovered since until now there have been no producers (thus, few/no consumers) of this interface.  However we expect this interface to become quite important in the near future, in support of rich text, complex documents, and multimedia.

A working patch is available.