You will face a problem if your network is high speed and or long distance. The failsafe baising is for self protection, not for driving a loaded cable. So by your method,when the line needs to be driven high, it will be driven by a low power drive of the failsafe circuit. This will not be enough to charge the cable/ network capacitance quickly. Because the 485 is a differential bus it cannot have low to high transition far slower than high to low or vice versa. Otherwise, the wave shape will poor, the "eye" will not be open properly, the reciever will miss bits .
Moreover you are assuming all the other devices in the bus will have failsafe chips, if not, even at low speed, the network will have marginal high state voltage.