An easy & very welcome quality of life option - Make multiple muffler / exhaust arrangement options available for tweaking the exhaust note for your car.
Diving into my own genre - Want a bit of an uneven lope? H-Pipe. Raspy but smooth high-RPM finish? X-pipe. Want to smooth either of those out? Turbo Muffler. Want to add some angry cackle to either? Glasspacks. Want a mid-ground non-descript exhaust note? Chambered Muffler.
This would be an easy customization option that could be integrated with no branding/licensing, it would mostly require a trained ear (or two) and/or a handful of enthusiasts to handle feedback