Apple is a too different architecture to adapt the driver from. Basically, you would have to throw everything away and rewrite it anyway - similarly with Linux drivers. Sometimes information can be obtained from the driver, but probably it's not that much and it's never a case of copy+paste of source code.
Our USB driver is based on a open source driver and much work was already put into it. We don't restart the whole process from zero again just because of a few not working well parts. This thing is very close to being sorta complete and another base won't change that at all.
ReactOS is still in alpha stage, meaning it is not feature-complete and is recommended only for evaluation and testing purposes