Currently, custom models set as chips can only use the default box collision shape. I understand that having custom collisions for stackable objects could be problematic, but I think sometimes other shapes are necessary for certain games.
Custom tiles can be used as stackable chips with different collision shapes, but they lack the detail that can be achieved using custom models.
My suggestion would be to implement something similar to the custom tile “type” system where the user picks a shape for the model (box, circle, hex, etc.), for custom models set as chips.