Hello,
I think it would be very useful to make a custom module extending a widget class. For example – I’d need to create custom widget extending MultiXy class to add some new feature: hold (& send probably) selected point on a xy pad. So I imagine that I’d need to extend MultiXy class by handle an touch event on specific point.
Unfortunately (as far as I know) you didn’t allow custom modules to interact with built-in for the sake of security. Would you like to consider allowing custom modules extending built-in classes?
I uderstand there is a way to do it by copying source code of needed classes into my custom module OR solving “requires” using browserify but I think it would be very dirty way to do it. Also, ability to extending built-in classes in custom modules not only could be a better way to do it but also wouldn’t allow custom modules to alter/interact with original code. Am I right?
BTW, great work 
regards, Teo