The new WriteFreely import functionality (T608) should also support plain .txt and .md files.
We should aim to be as flexible as possible in supporting writing from other sources. Some users might have a cache of plain text files saved on their computer that they'd like to publish -- we should support that.
Allow users to select multiple files of type .txt or .md. Parse each one and publish it as we do with the txt files from a ZIP import.
Prior art on publishing text files via the API: https://github.com/writeas/writeas-api/tree/master/examples/go-text-importer