Will you be adding this feature ?
depends on exactly what you mean…? But the answer is “yes, probably”!
well all Components have properties in a ValueTree, it would be nice to set them in a RAD like Jucer, so that users (not programmers) can implement some custom behavior for standard components, the properties will be interpreted by a library that uses such component and will be able to implement the desired behavior without any additional code.
In my case UI components like Sliders/Combos/Buttons need additional information (midi mesages type, controller number, sysex byte data) to implement a fully working device editor. I simplified my library to take a pure JUCER component, but i still need an additional XML file to tell the engine about the midi stuff, if that could be done in one RAD it would simplify things very much.
hope i’m clear about my intentions 
Yes, totally clear - and yes, I’m certainly going to add something like that!