It's possible to open 2 or more workbenches at the same time, however...
This becomes increasingly more difficult on lower end computers and more complex situations.
This also would require having 2 layers in the world editor so saving would work.
Also requires clients to have higher resolution or more than 1 display.
Therefor, this is a bad solution.

Something like tabs in web brwosers would be a desired alternative.
Having multiple tabs for object properties window and also allowing creating more than 1 window of object properties would be desired.