First of all, we should think about what is Wikibooks made for: reading books or writing
books. Your idea is not bad for the first purpose, but fails when we focus on the second
one. My opion is that we should not make Wikibooks look like a 'conventional'
book, because this will complicate creating and improving our textbooks.
Remember Wikibooks mission: we do not host ready books, we are a platform where books can
be created and improved; this process never ends. Wikisource is for finished materials.
When someone wants just to read our textbook, we give him "print version" - all
chapters in one, no sidebars and obsolete elements. I think our print versions are quite
decent; I don't understand what's wrong with
http://tools.wikimedia.de/~magnus/bookmockup/book_now.png; in my opinion it is great.
When it comes to sidenotes and sideimages (never seen such thing), I'm against them.
In the example you have given, they only narrow place for text and look odd; textbooks I
use in most cases don't have such things.
Regards,
--
Piotr 'Derbeth' Kubowicz
Jabber id: derbeth(a)jabber.wp.pl
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