[At_Libitum]

Originally Posted by skreutzer

The question is, if Sigil could become this software, since it is already specialized for such kind of tasks. Unfortunately, Calibre is going into the opposite direction, making Calibre output less usable.

In what way? It is my understanding that Calibre's book editor is to be similar to Sigil in lots of ways. And since Sigil is for all the good intentions and purposes, dead as far as future development goes, I would have expected Calibre to be the more logical choice seeing as its Edit Book is still very much in the early stages (even though what currently is available has been implemented in record speed/time) and therefore likely easier to adapt to your needs. In fact, from what I understand with my limited scope from your post, the functionality you speak of could maybe be put to use as enhancements to the same.