> A combined MPU and MCU architecture isn't that exotic. ST microelectronics currently sells a single chip with that contains a two core Cortex A7 Microprocessor combined with a microcontroller. Admittedly more tightly integrated with ability to communicate via shared memory.

Don't underestimate the value of that integration.

With the hybrid architecture chips you get the vendor controls for managing the MCU with supporting documentation. ST is good at this.

This isn't the same thing. It's two chips running side by side. It's possible to set it all up so that the Linux chip can control everything you need to manage the MCU, but it's not easy. There are a lot of edge cases to think about and things that need to be handled manually.

> A combined MPU and MCU architecture isn't that exotic. ST microelectronics currently sells a single chip with that contains a two core Cortex A7 Microprocessor combined with a microcontroller. Admittedly more tightly integrated with ability to communicate via shared memory.

Going with an SoC is much simpler than trying to set up custom communications between two processors, I'm not sure why they didn't think of that.