> What I would love is a simple standard for aftermarket radios, like you used to have. One connector, and it wires up to the speakers, a display (that you can replace), and all the hardware buttons e.g. in the steering wheel. You'd have a one-way connection from the car to the device for information like speed.

That would be nice, but unfortunately it has a number of drawbacks:

1) "one connector" does not work well with today's 20+ speakers

2) display interface? Either you do it using DSI as interface (which is fucked up so bad that a Raspberry Pi supports exactly one specific type of display - and when even the Pi hackers can't get it done, I seriously doubt car makers can), or you use HDMI which will lead to vibration issues. Furthermore, the range of display resolutions, aspect ratios etc (you can have anything from 320x240 to retina FHD)... no way ever that radio/car makers will implement this.

3) Interface to rest of car (HW buttons, speed feedback, and maybe even GPS/IMU for navigation): no standard for this except CAN-bus, which is a security hellhole itself...

I agree that having the option would be nice but it's a real niche market.

I don't think it is that unrealistic. It seems that for 1), aftermarket radios are available for most cars and can utilize the speakers. There are various adapters available. For 2) I can imagine HDMI or DVI, if necessary with a more sturdy connector. Stock monitors have supported multiple resolutions for 20 years. For 3), it seems there is information available to access this from CAN or LIN buses or ODB. Lots of hobbyists do this. I can imagine you could buy an adapter for, say, "Ford 2010-2014", like you can do with various aftermarket parts.

It might be a niche market, but so are all kinds of aftermarket mods for cars. And I think if somebody did to car stereos what Nest did to thermostats, it would be phenomenal.

FYI, HDMI has an automotive connector (type E) as part of the specification, which is available from a range of manufacturers already and has a retention clip to avoid vibration issues.

Sidenote: Some cars still use composite interfaces, because with a reasonable comb filter it doesn't look too bad, and it only takes one wire and ground.

Thieves have largely stopped breaking into cars to steal car radios because, without a simple standard for aftermarket radios, the market for stolen radios shrunk and has almost disappeared.

Actually, that is very hard and also without any benefit for car manufacturers.

They could advertise support for the Bose/Sony/Apple/whatever premium entertainment system; a standard - even a very basic one - might also reduce development work, as you can use preexisting connectors etc.

And, at least for me, if I would buy a new car, repairability and replaceability or parts is a consideration. And if I had $1000 to spare, I'd buy a hifi unit from a dedicated manufacturer - and would prefer a car vendor that makes that easy. I've never heard the entertainment system be the decisive factor in choosing a car - but I know people who put off buying an e-mobile because they usually have annoying computers built in.

Finally, I don't think the car vendors would neccessarily do this. You'd probably have third party vendors selling adapters. Crazy cable tree in, nice plug out.