Yeah, a lot of wireless routers would have no trouble. A lot of them do in fact have MMUs. I wonder if you could get Busybox running on an ESP32? Probably not most 8051s, though, or AVR8s.
Looks like the ESP32-S3 model works with modern Linux (it's so bloated compared to the old 2.0/2.2/2.4 branches...)
The other option seems to be Apache NuttX as an RTOS (runs on all ESP32), and then Busybox w/hush or Toybox w/toysh. The more shell features you need, the more space it's gonna take, but technically 64 kB flash is possible.
The other option seems to be Apache NuttX as an RTOS (runs on all ESP32), and then Busybox w/hush or Toybox w/toysh. The more shell features you need, the more space it's gonna take, but technically 64 kB flash is possible.