The orange lines show the new main tube postion, leaving room under the tube for the one remaining joint. But this is bad because it raises up the rear part of the seat by 2". Not what we want to do. Unless we can put the hinge THROUGH the new main tube. Nah. that won't work.
Another approach. Let the new design morph down even more. Then adjust the head tube angle up to compensate. Need to check the result in the up mode. Don't want much negative trail there.