Doyon, I am fairly sure what you are asking, but will try to explain why it will not work.
We use a number of the Advantech Adam modules at work. Example is that we have about 6 of the 4018 Analog devices on the same serial port. Addressed 1 - 6 and if I give a write command to #1 and then without waiting, a command to #2. There is a strong chance that #1 will start sending while I am sending the command to #2. The RS-485 does not have a good hand shaking system like RS-232. And even if it did, there is always the chance that the propergation time delay from the closes device to the furtherest device might negate the handshaking. RS-485 can be 4000' in length. And note, RS-232 is what? 30 feet at most.
So, in a nutshell, no handshaking per say. Long cable runs can even negate a wired handshaking. Also unlike TCP there is no packet like loss of message checking. RS-485 is more like UCP message transmissions. And due to all of the above, is the reason that there can only be one master station / device. And I agree with all of the above posters trying to illustrate that you will more than likely get a mixed message containing both the reply from #1 and #2 device. So this leaves us back with sending out a query of device #1, wait for the reply and then sending out a query to device #2 and wait for the reply and so on for each device.
I agree with the hive mind. Might look at ethernet devices or maybe USB (no personal experience) for a solution for your needs. BTW the Adam 4000 devices also have a 1 sec. max scan rate. Just to illustrate that some devices have a slow update rate.
