I was the "scorer"
Sorry but i still thinking that your idea is not good. May be i can say better that "is not useful" than is wrong because is not wrong.

Why i think is not usefull:
- A soft uart is slow so a 10 uart at the same time will be slooooooow
- As option i suggested the use of a external hard UART
- You say that he implement put some protocols.. but may be he can't if the 'slaves' devices are done
- You say is 'cheapest' and i think as some one says: "Cheap is the thing that you know how it cost before starting" and may be you know the components cost but you must design the PCB, and the soft and make all work
- The PC soft must be special and you can't use the standard programs like i.e. flip or others.
- May be you have solved all thouse problems but i think is not easy for others to do that.


Best Regards
Félix Díaz