Maybe using an ARM dev board boosts acceptance of this book among its target audience, at the moment. But, for open source hardware goals, a RISC-V board, such as the HiFive1, would be good cross-promotion/support.
Similarly, as long as Rust is already shaking up C/C++ a bit, they could nudge some hobby/education and professional development towards RISC-V. (Especially on embedded, right now, as I've heard the open ISA is attractive to some projects.)
https://blog.adacore.com/ada-on-the-first-risc-v-microcontro...
https://hackaday.com/2018/10/08/programming-a-risc-v-softcor...
https://riscv.org/2019/01/adacore-joins-the-risc-v-foundatio...