I was thinking more about devices that can be repaired by changing a failed CPU than devices that have a lower failure rate. I believe STM (and others surely) h

I was thinking more about devices that can be repaired by changing a failed CPU than devices that have a lower failure rate. I believe STM (and others surely) has a line of "process critical" MCUs that may have additional reliability features but these chips are built in much lower quantity and are much pricier. It's a tradeoff that would need to be evaluated for sure. Preferring external flash to on-chip storage would also help. Some ECC can also be performed in software where warranted.