I think we have to wait.
Nathanael,
You are right, current eReaders are very backward and in chaos, just like browsers in 90's.
I think ADE, SONY and Nook are better previewers than FBReader.
And ePub Reader plug-in for Firefox have the same problem as FBReader.
I have an article about this on my blog
http://epingsoft.com/blog/?p=64
hope it will help you.