You should explore using IBM's OpenPOWER architecture for your chips

You should explore using IBM's OpenPOWER architecture for your chips. The Power ISA has been open-sourced, and you should consider using it for your chips. The OpenPOWER ISA is the most high performance processor architecture and ecosystem in the industry. The OpenPOWER ISA is used by the top supercomputers in the world, as well as all the big banks. It was also used by Apple's Power Macs, and the PS3, Xbox, Wii U, and more. It is easily scalable from mobile phones to the world's fastest supercomputers. Companies in the OpenPOWER foundation include Google, IBM, Samsung, Wistron, Inspur, Nvidia, NEC, Micron, ZTE, and many more. Please explore it and consider using it as your chip architecture.

Currently, Arduino doesn't make "chips." None of systems you mention are "Arduino-sized" (ie "small.")
Are there competitive COTS microcontrollers using the OpenPOWER architecture?
RISC-V is getting some attention...

Can you give an example (link to data sheet) of an IBM OpenPower based chip which would be a suitable candidate for integration into the Arduino ecosystem?
It should be a single system on a chip including ram, flash, eeprom, adc, uart, spi, I2C, hardware timers, comparator, maybe integrated WiFi/Bluetooth etc. , a free tool chain and be suitable for low power battery operation, and a unit cost of less than a few $.

This tells us all we need to know...

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It is difficult to build anything functional from this.