Multi-part supports

I often would like to print several large parts at the same time. I layout the parts so no collisions will occur, but they are often overlapping vertically, such that when I generate supports, the supports collide with parts lower on the bed (and Preform correctly warns me of this condition). Generating supports which account for this and provide appropriate break-off points on the top of the lower part and don’t double up on supports between the bed and the lower piece would be very beneficial.

This is a tricky one. While breaking off the supports under the part is probably doable software-wise, you’d also have to be able to ensure that the part the supports now start on is strong enough to support the building of the part on top of it.