Hey Guys, I am in the same boat here. Currently have an X3M and planning to move to a G80 M3 within 6 months. Bike rack on the rear is an absolute necessity for me.
While I can't see anyone has listed a tow bar yet (or tow hitch as you yanks call them) I don't think the exhaust placement is the be all and end all.
Have a look at the M340i's they run a very similar rear muffler, yet Stealth Hitch have had a product for them for some time.
https://stealthhitches.com/products/bmw-hitch-shr31003
We may find that the chassis is very similar and they just haven't had the demand yet to build one.
I'll reach out to see what they say, if I get a non committal response we may all have to email them to show demand. Worst case for me is I may try to adapt one for a M340i.