* Table of contents: solved by Pandoc.

* Inserting special characters: personally I don't find those "character choosing" windows to be very convenient. Hunt and peck is a slow way to type! Anyway, you can do this in Markdown with either Unicode (if you have the right keyboard) or you can write HTML escape codes (&tm; etc.)

* Automatic (grammar/spelling). I don't like check as I type, but sure. Anyway, Emacs provides this if I want it.

* Macros. Hello? Emacs? (Also, Pandoc has a scripting interface.)

I may not be published yet but I've written my own book. I've also published books for other people. I did both of those with a Markdown-based toolchain. It works.

Edit: Just to prove the point: https://www.amazon.com/dp/0692553916 . Go see for yourself how the book is formatted.

Pandoc is definitely the way to go in terms of ease of writing and the quality of the output.

It's not super difficult to take Jekyll-ish input and generate books from it either, e.g. I built a tool to do this:

https://bitbucket.org/elliottslaughter/bookmd

Example of a book I published with this approach: https://www.amazon.com/dp/0692553916 (a fairly challenging type setting problem with lots of footnotes, foreign language, etc.)

The main gotchas are that if you really want it to look good you have to dig into the Latex template, so ultimately it would take more effort to make it push-button for non-technical users.