Right now moving units can be any size, but are square - they have an implicit cellmap that is all 1s.
The feature request boils down to allowing a moving model to specify a cellmap.
It would be ok for the path-finding to take into account only the unit size and not the shape of the cellmap, and it would be expected that its unlikely that other units can move easily through holes in a cellmap since the random angle means that each cell in the map might occupy more than one tile on the board.
But within those confines, it seems like a very good generalising of the engine and would allow the use-cases given in the original post, namely ships.