Jeremy K.,
I agree with your suggestion.
On the other hand, though, what about enabling customization of hot keys not only for macros, but for Handouts, specific Jukebox sounds, and other items as well that Roll20 handles?
I'm saying this because macros, while very useful, aren't per se the only or the first priority for all games; right now there is a variety of features and game assets, and the Roll20 app being suitable for very diverse uses and play styles, could be even more flexible by means of such "open hot keys customization".
Just imagine a sound-based game or a RPG system in which instead of making the suitable dice roll for a particular situation (by means of a macro, for ease of use and speed of access), the GM asks you to play the right sound between a number of possible ones: in this scenario, hot keys for Jukebox's items would be suitable as well.