I think there will always be applications where an OS is not needed, but 32-bit micros with floating point like the STM32-F4 (~168 MHz ARM) can do a lot of cool

I think there will always be applications where an OS is not needed, but 32-bit micros with floating point like the STM32-F4 (~168 MHz ARM) can do a lot of cool stuff that's impossible with Arduinos. Nontrivial robot state estimation and control, for example.