The old book view had its own problems which were very annoying. Things got automatically highlighted, so when you pressed delete more text than you wanted disappeared. But syncing, such as it was, was nice.
Please do not drop book view. It allows me to see if my code editing has been successful or not without having to open up another program. Half the utility would be gone, since if all I wanted to do was edit code I could use tweak epub along with any good text editor. Being able to find odd characters or strange spacing is very worthwhile. PG Canada material has page numbers made invisible that cause odd spaces in the text. It is not easy to see this in code view, but it is very clear in book view. The effect of non-breaking spaces is more obvious in book view than in code view. It is hard to keep both BV and CV, but it is worthwhile.
The syncing issue may not be such a big thing if we could see the position remembered in book view. I usually work my way down a document, so I would generally move down both on the BV side and CV side pretty much together anyway.
Any chance the BV modules old and new could be modularized, so they could be selected at install time, without creating much more work and hair tearing? Maybe that would satisfy both camps.