Suppose you took a SPD pedal that has a cage like a quill pedal - Shimano M324 for example - and attached toe clips with loose straps to the SPD side - in other words, to clip in you insert your shoe into the clip then step down.

Would this work?

Why bother? Two thoughts. First, maybe you want the choice of riding in either clipless cleats or in non-cycling shoes plus the added security of toe clips. Second, maybe you have a vintage bike that just looks wrong with clipless pedals.