The other problem i see with this is that another attachment further jacks up the cost and the complexity of designing the controls. If you have four controllers and want to play four player Warioware 2 with WM+/NC+ support you are looking at shelling out a ridiculous amount of money all up. 4 wii-motes, 4 nunchucks, 4 WM+ 4 NC+, i don't even want to do the maths.
As a developer you would potentially need to support regular Wii controls, WM+ controls and WM+/NC+ controls. Sounds like too much hard work for most to even bother.







