Closed source and un-modifiable car firmware is like closed-source crypto and other systems - it's not the best. Because it doesn't really have to be better, so why bother. Open source / custom can be as bad or worse, or it can be much better.
I prefer a world where we have the freedom to have good stuff.
Anyway, you can already mess with modern cars tire pressure sensors, when driving near them. http://www.winlab.rutgers.edu/~gruteser/papers/xu_tpms10.pdf
Closed source and un-modifiable car firmware is like closed-source crypto and other systems - it's not the best. Because it doesn't really have to be better, so why bother. Open source / custom can be as bad or worse, or it can be much better.
I prefer a world where we have the freedom to have good stuff.