F1 uses wheels for the grid position and bodywork for the splits/finish? If anyone was gonna do it, it would be F1 I guess - I've seen their idea of what constitutes overtaking
I think we need to have the grid spots and the splits/finish measured with a consistent method, and that bodywork would be better than wheels for general use. BTCC regs are by front-most bodywork (
3.6.1).
I've seen a fair few ties-to-the-hundredth broken with screenshots, they were all by bodywork as far as I can remember - it seems well-ingrained. Also, F1 gets to cut the discrepancy between the two measurements by regulating nose length, but we have massive variation of mod geometry to contend with.
I guess there'd be quite a bit of extra calculation going on to find the front-most part of the body in the direction of travel. I don't know enough to know if that's too much processing to be doing every frame, but if so maybe it could be generated at pit-out (with later damage ignored) or limited to LOD3.
(I'll stop waffling now, I'm getting into premature optimisation of code I don't have to optimise

)