The things to do are:
1. To make VisualEditor support the separation of Page: pages in header/body/footer/level. I believe it is possible to implement it without having to do hard modifications in the VisualEditor.

2. Add support for Wikisource specific tags (<section>...).

So I think it so it would be doable only by a skilled person, definitively not by a GSoC student.

About the amount of work, I don't really know. Something around a month for an experienced developper would be my finger in the air estimation.

Thomas