Some people have done it.
Linux_fan did it on his build, but I believe he is reverting to a single ATC spindle.
Ger21 is doing it on his current build I believe.
I don't actually know how to control more than one Z axis in generating the G-code or running the machine software, I just know it's possible.
If I was going to do it, I'd probably ask Ger21 how he's doing it and go with that.