I'm working on the joystick type now. It's got some strange bug I've been unable to find.
If you look at the USB code, you'll see I'm trying to use a more modular approach, but without a lot of the complexity of some other traditional USB stacks. At some point, that'll make it easier to mix-and-match various USB stuff... and of course having lots of endpoints makes it possible too.
In the short term, I'm planning to do joystick and midi, and of course serial, keyboard and mouse are already working. Then I'm going to focus on porting more arduino libraries and writing better documentation. That's really needed more urgently than more USB options.
I do have several usb types in mind, but serious work on those probably won't happen for at least a few months.