It may seem simple but moving more than one at a time bumps into a host of basic game bedrock coding........ The game was designed from the beginning to deal with "one unit at a time".... that's why only one aircraft can enter, make an attack run and has to leave the map before the next one can make it's run-in.
Move a stack of units and it's opfired on would require a significant code adjustment with an unknown number of knock - off "gotchas". 
After tweaking other peoples code for almost a quarter century the desire to re-invent the wheel is not as strong as it once was 
