Saying that Apple will do this because they are using a coprocessor is like saying Apple was going to run Mac software on 65C02 because the IIFx included two 65C02 processors.
But during the PPC transition, you could buy a PPC daughter card for 68040 Macs to run PPC software but you couldn’t use them simultaneously.
But during the PPC transition, you could buy a PPC daughter card for 68040 Macs to run PPC software but you couldn’t use them simultaneously.