the robots would be overpowered, because robots can just sit on the cart and they keep respawning in waves, witch means that there would be a giants at the cart and everyone would have to go pyro to blow them off the pl. and red has a whole thing where the cart can move back because in pl maps, when the pl is not pushed there is a 20 seconds before the cart moves backwards, witch means the reds can win easily, unless the 20 sec. pauses after the/a wave has been completed, witch would take a lot of coding. and if a moding group had this to work, then it wont be noticed until someone looks up this topic again. witch would probably be a year or 2 after it was accomplished. unless if valve did it, then it would be popular
edit: still, valve wont do it because they did say they were making enough money from cs:go,tf2,ect
edit 2: and i dont think someones gonna actually do this.i know a guy who was working on a event map for 4 years, so i think making a whole new gamemode would take 5-8 years to make something like this
edit 3: valve also had a new gamemode prepared and everything and they threw it away for a reason that i dont know