Is mbed RTOS suitable for commercial motion control solutions
Yes, Mbed OS uses CMSIS-RTOS2, which is built on top of Keil RTX 5. This is totally capable of doing hard realtime.

Regarding network handling, it depends on your requirements. If you need full, 100% timing guarantees then a network handler which might trigger an interrupt will cause problems, and splitting it up could be good. This would be something best measured first.