Specification needed for dictionaries and other reference works
One of the shortcomings of the EPUB format as it is now is the absence of a clear specification for reference works such as dictionaries. This lack (in my and others' opinion) is preventing publishers to create dictionaries in the EPUB format, which in turn means that reading devices supporting EPUB usually don't support dictionary lookup.
In the MobileRead forums there has been some discussion about this issue, and there's even some proposal for extension of the spec here.
I believe work on such a specification should be a priority for the next revision of the EPUB spec.
Moving to "future consideration", but there is much agreement in comments, so a creation of a short-term informational document should be considered.