> No footnotes or endnotes;

I must be misreading that. How is lack of support for footnotes and endnotes a positive feature, as opposed to a glaringly missing feature?

> saving the compiler the job of managing complex code.

I re-read this 6 times, trying to figure it out. You mean, the human who creates the book?

On technical forums, I suggest you not use "compiler" in that sense, because we are accustomed to its technical meaning, of software that translates computer language.

On a positive note, I like markdown, and I dislike creating and reading XML by hand (although it works ok for software to deal with), so this seems like a fine idea to me.