> Download 3rd-party firmware for your car?

I imagine insurance companies will eventually have clauses that prevent this.

They don't prevent me from modifying my car now. In fact, they'll explicitly give me coverage for aftermarket equipment upon request.

"Evenutally". There's little reason now, with 99.99% of cars being human driven, where a dropped Twinky has a higher chance of causing an accident than some slightly modified ECU curves.