To be fair, there were some quite serious discussions going quite far beyond "implement GeoMod somehow", so we may someday reach the point where it stops being just a running joke.
Is it impossible to generate the effect of interior structure on the fly, as part of the shader somehow?
AFAIK, shaders mostly affect textures and lighting, I'm not sure if they can change the actual mesh.
there are geometry shaders actually, but they are fairly new, and i dont think the engine is set up for them just yet. we have given geomod some serious thought though, there was a thread in modding about it. the idea was to log your gashes to a data structure containing the dynamically generated gash mesh (this is just a few polies from the model and remapped), the position and normal of impact, what hole model to use, its transform data, etc. you use independent hole models, which could be defined by ship, by species, by weapon, etc.
a gash would contain a small subset of the surface polies that were intersected by the damage radius of a weapon, with a greyscale damage texture and planner uv projections (projected along the impact normal) applied. this would be rendered to the stencil buffer (i thought about using a sprite but it would look crappy). you would render the ship normally, and then you would render to the stencil buffer, and then you would place hole models in the logged impact locations, and using the stencil buffer as a mask, render the holes. the result is a composite of ship and hole models.
the holes would be manifold meshes, so when rendering them you would need some way to clip them, as parts would be sticking out of the model. i figure theres is some fragment shader magic that solves this problem. all i could think of was to use a second z buffer when rendering the holes (as you dont want to overwrite the z values for the hull). toss fragments behind closest hole model fragment (as usual) using the value from the second z buffer, but also toss fragments that are in front of the hull fragments (value from main z buffer). if these two conditions are met, render the fragment to the frame buffer, with regards to the stencil buffer. after ships and their holes are rendered, you somehow need to copy the second z buffer data into the stenciled area, after that you can reallocate the stencil and second z buffer to other uses. i dont know the details well enough to know if this will work, my opengl skills are still in the stone age, everything ive done thus far has been fixed function stuff.