Answers inline.
> Does FileTransfer implement any published standard, or is it our own API? > > Nope. > Does it make sense for FileTransfer to continue to use raw FileSystem paths > (and *not* go through File at all?) given that the File API will soon be > returning only relative paths and filesystem:// URLs. > > Consistent w/ URL scheme makes sense to me but I'll let others chime in how this will break everything and our users will hate us. But remember: plugins are versioned!