Uhhhh.... Qt is a graphics toolkit, not a programming language.
What language are you suggesting be used for the logic (database code, device interfaces, content server, etc)? Because you mention HAIKU, it is probably C++.
Rewriting calibre in C++ would be a multi-person-year effort. In the end, we would have something that might or might not be appreciably faster, but *would* be harder to maintain, harder to develop, and harder to debug. Hard to see why this would be a good thing, but perhaps I am confused.
