A nice Sigil feature was the ability to have 'Templates' with placeholders that would be changed at insert time:
http://web.sigil.googlecode.com/git/...add_cover.html
[Insert Cover] and if cover.xhtml was in the user's AppData folder, it would be used instead of a 'generic' xhtml
It might be a useful feature to have templates xhtml files for Cover, TOC, New, Title, etc.
Something like
[Insert Special ...]
Cover
Title
TOC
New
browse ....
The Sigil Cover template had 3 placeholders ...
SGC_IMAGE_FILENAME: this will be replaced by the path to the image in your EPUB.
SGC_IMAGE_WIDTH: this will be replaced by the width in pixels of your image.
SGC_IMAGE_HEIGHT: this will be replaced by the height in pixels of your image.
but possible the different 'specials' would have their own as appropriate
You can insert a file now of course, but the benefit IMHO would be the place holders and the generation of the semantics (I think that's the term for saying "This is the Cover")