Our project has been using Qt for four years, and the majority of our company’s income is currently based on releases from that time period. But, Qt is really buggy when using your code in VST/AU/RTAS plugins, and juce is a tried and true audio/gui/plugin library. We are considering porting our entire gui code base from qt to juce before what will be our flagship product, and incrementally porting the code while also being able to enable and disable support for each ported feature, code compatibility is going to be key.
It occurred to me that one feature that all platform-independent gui wrappers should have is to create a drawable widget based on a native window handle. This enables you to mix gui frameworks, and would also make it very easy for us to incrementally port our code from juce to qt. Currenly, juce does this very well, and Qt does this very poorly.