I tried the 0.1.11 and I have seen great progress.
I could nicely process text files. The extension requires the .odt suffix to be present if not it refuses to work.
It's pretty quick and precise for the text. You present an external stylesheet which is quite clean (uncluttered) and easy to modify which is quite useful. It's still incomplete though (some styles are missing).
As you said I've got no results for images.
Your proposal to complement it with Sigil for the time being makes a lot of sense. Sigil is excellent for inserting images, building TOC and filling up some meta-data, so...
Congratulations for your progresses. I think that, due to the existence of Sigil, the priority should be to focus on the missing "text-related" features, like footnotes, links and identification of some special styles like quotations, poetry, horizontal lines,..
I forgot to say that the automatic splitting and the creation of an external style sheet provided by your extension saves later a lot of time because these features do not exist yet in Sigil and have otherwise to be processed "manually".
As far as styles are concerned, I think a reasonable middle ground would be to provide first full support for what OpenOffice.org calls "html styles".
To go further, the user must be warned that he has to exercise some discipline and restraint before committing himself to produce an EPUB. Very often the multiplication of "automatic styles" comes from a user's bad practice (like using "select all" to modify text attributes) instead of strictly committing himself to the use of Stylist.
Very nice work.
