I've always considered Topaz to be a format with potential, despite its very definite flaws and instability when actually used.
The problem with it is that people don't use it to make the sort of ebooks that aren't possible with Mobi:
- stuff with carefully arranged images amongst the text like certain illustrated editions,
- anything requiring fancy typographical layout like some forms of poetry,
- foreign language and invented scripts not covered by the current set of fonts which would look very bad rendered in tiny little inline gifs,
- books with complex data tables in them that turn into squinty unreadability under Mobi's max 128kb image rule (would need a zoom and pan function, though)
Also, the format is kind of lacking in standard e-reading features (I've never seen a Topaz book with flickable chapter markers and many seem to be missing Tables of Contents), and would also be vastly improved if the makers could only link a proper corresponding text version to the book instead of the auto-OCR.
In fact, it would be nice if Topaz were a bit more like DjVu and people could opt to see the scanned book as-is, and also view a proper plain e-text redaction if they choose. Maybe even be able to toggle the display between the two.
In any case, I'd like it if Amazon were to one day release tools for ordinary people to make their own Topaz books, perhaps starting from a PDF or SVG document.
Because there's a lot that could be potentially done with the format, especially if Amazon remains adamant about not supporting ePub while also not improving Mobi; it's just a shame Topaz mostly gets used for books which don't need it and its more useful features do no one any good.