Sorry, for now we have what we have.
If you need fields from book library move to other VirtueMart fields - you may rebuild that through code. Book Library Open Source/
Also you may write to Ordasoft support form and ask custom version with all features what you need.
exactly so as you describe - good have for Book library self - when user may select what fields fetch from Amazon to what filed in Book library.
But that require much work, and I afraid will need only for 10% customers.
Main users prefer take excellent site and do for that as small config operations as possible.
All look like now for customers need create very simply components