Subsystems can have debris, I suppose you could mock something together by using a lot of clever modelling and texturing, it's possible that way, but to be honest, the outcome wouldn't be work the effort involved in my opinon.
Geomodding, i.e. physcially altering the main hull mesh is currently impossible, and, to be honest, apart from a few exceptions, usually strikes me as being more work than the results are worth. It's ok for things like walls in FPS/RTS games, but personally, I think something like Bobb's damage decals coupled with subsystem debris would probably work better in the long run.