>One way out of this is for the major OEMs to band together and create their own standardized platform that works across OEMs. At minimum, that platform should expose a single standard interface to all third-party service providers.

This already exists, and it's why there's a slew of Bluetooth-enabled apps on the app stores that let you self-diagnose your own car. It's called OBD-II and it's federally mandated on every vehicle since 1996 in the US and since 2003 in the EU: https://en.wikipedia.org/wiki/On-board_diagnostics