No. For very good reasons.
You can, however, do an export to InDesign, make a custom PDF, and use our Upload writing mode to upload.
However, unless you're making a coffee table or art book of photographs, landscape mode is a bad idea for books.
When you think about screens, there are lots of smartphones in the world, so making a book in landscape mode would mean it would be terrible on phones. Portrait mode is far superior on phones.
Furthermore, in Preview and other PDF readers you can read books in Two Pages mode (which is most like a traditional book, in which you also see two pages at once), and in that case portrait mode is better as well.
Finally, with a computer programming book, you can just open a PDF in single page mode, and then follow along with the book while coding.
So, in all cases except where the book is a coffee table book, Portrait mode is better. And a coffee table book should be designed in InDesign anyway. So, we only support Portrait modes for books.