Maybe you could that a look in the minnsh PoC, it was running on MCU with less than 16KB Flash and 8KB RAM. As you can see in the image it is using less than 2KB RAM:
To get to the minimal size, that configuration also depended on the ability to disabled file system support (and, in the longer run, on the development of a HAL). There is no HAL and the option to disable the file system has been removed.
