Would it be possible to duplicate an object by holding down Command or Option *after* you have started dragging the object?
Currently you have to hold Command or Option down *before* you select and drag the object to duplicate it. Coming from Illustrator, this is a slow and painful muscle memory to remove as you have to stop, undo, then start again (times one hundred).
I can see how Illustrator and Designer handle object movement differently, so this might be a big change. Here is an example of how it could work using the current (visual) drag method.
1. Start dragging object
2. Hold down Option/Command
3. '+' icon appears over the original (currently dragging) object and a copy of object re-appears at original location.
4. Release mouse button first and both get locked down. Release Opt/Cmd first and only the drag is applied.
Love your work :)