The initial Feather file format is a minimal subset of the Arrow IPC format. It has a number of limitations (see https://wesmckinney.com/blog/feather-arrow-future/).
We want to retain "feather" as the name of the on-disk representation of Arrow memory, so in order to support everything that Arrow supports, we need a "feather 2.0" format.
IIUC, defining the file format is "done" (dump the memory to disk). Remaining issues include upgrading "feather" readers and writers in all languages to support both feather 1.0 and feather 2.0. (e.g. https://issues.apache.org/jira/browse/ARROW-5501)