i'd less likely use stm8s as 'standalone' mcus, even though they could do that. the main reason is that with 8k flash and 1k ram
http://www.st.com/content/st_com/en/pro ... 103f3.html
it would be quite a challenge to do partially what we are doing on stm32
however, it is a 8 bit device and hence would be more 'memory efficient' vs stm32
my thoughts are that they may make good 'delegate' mcus / subsystems working in conjunction with stm32
take for instance a 4x4 key pad, this would take 8 gpio pins (of course i can use resistors and do analog reads but that has its own disadvantages). i've thought about using shift registers but it would take 2 basic logic ic one for parallel to serial, the other for serial to parallel, takes more board space, more components and does not really reduce the interfacing pin counts to the main mcu.
in this case if space is a premium and fewer components counts is desired, stm8s could really function as a 'delegate processor' and perhaps interface the main mcu on i2c lines which takes just 2 pins. i'd think there are more use cases than that e.g. motor control delegate as each stepper motor possibly use 4 pins, sensor delegate, comm delegate etc
Anything not related to STM32