Car companies are terrible at making software. I'm not surprised that they want to lock down the ECU code, since it's probably awful and full of subtle bugs as well, and they don't want to get hit with tons of lawsuits when people find a bug in the firmware.

Really wish they'd just use CarPlay / Android and go back to analog knobs to control HVAC stuff. Opening a modal dialog to adjust fan speed (in a 2015 MDX I've been in) is terrible UX and very distracting to do while driving. The 2nd gen Prius is no better, and the control panel UI in it looks like something from Windows 3.1.