Awesome! A clock-independent Arduino core would be great. There are a few other clock-dependent routines in there. One is the analog read configuration: the prescaler value should depend on the clock speed but currently doesn't.
We are planning to support different hardware configurations (maybe even non-AVRs). Probably not in the sketch itself, but by providing a menu with a list of options like Arduino, stand-alone ATmega8, Wiring, Crumb, whatever. Those menu items would be defined by configuration files in a directory somewhere, in a format easy enough for someone to define their own.