Currently eBook Publisher does not support many many special glyphs, of the kind used in phonetic transcriptions (e.g. pronunciation guides in dictionaries) for example or the special characters used in writing in Esperanto (i hear...) and presumably some other languages.
It would be nice if the next version could support a wider range of properly coded unicode characters / html entities ; the only thing more frustrating than seeing
"Unknown named entity (& thorn ;) encountered. Replacing with '?' "
in the output window, is seeing
"Legal Unicode value encountered for a glyph we do not support. Replacing with '?' "
Additional font support would be really nice as well ; even if only Arial and Times New Roman were added, the glyph support would probably be pretty exhaustive from them alone, and in addition these are good basic fonts for formatting body text which also have true bold and italic forms (this is important).
Ideally, it would be really brilliant to be able to load your own choice of True Type or Open Type fonts ; apart from the comfort and pleasure of reading a really well-drawn font, this would also allow you to support whatever glyphs you needed by simple adding the proper font.