Yes, this can be modded to USB load games.
That adapter makes a GameCube look like a Classic Controller to the Wii (it connects to the bottom of a Wii Remote the same way), so currently, this won't help in getting GameCube game support on this model of Wii.
The Devolution people are working on getting Classic Controller support. Once that's working, then what you're wanting to do might help. But until then, you would only be able to USB load wii games.
Link to the Softmod Any Wii guide is in my signature.