Or are you talking about a queue that you would set and it would set the queue in multiple individual cities? If that's the case, then no thanks.
When I go to war or when I get DOWed, I need multiple different types of units and I need them all around the same time. So one city builds Infantry, another builds Artillery, a third builds Armor, etc. With one queue that set the queues in multiple cities, I'm building the same thing in ever city. So instead of being able to go to war after a dozen turns because I have the diversity, I have to wait for 30 turns before I have a massive army that is cumbersome to move and slows down my march thru enemy territory.
And yet again, what are you trying to say? Whether I have three cities or 30, they still have their own needs and advantages. Sure there will be multiple cities that produce gold and multiple cities that produce units but they will still have different needs at different times since they were built at different times.