Switching to blue+green LED wouldn't be that easy, as You would have to make a separate switch for the LEDs, synchronised with phosphor wheel controller.
All this in order to emit blue only when blue is required, then only grenn when required.
I guess in no color wheel DLP projector, the sources are switched on sequentially, with green being a result of blue emission + proper phase of phosphor wheel.
Piotr.K