An open problem for "falling block applications" in 1.18: If you have a falling end portal, then you can make a flying machine that automatically places down a line of end portals. The idea is to always use the previously placed end portal block to place down and dupe the falling end portal at the next position. You then need to transport the falling end portal back to the flying machine and repeat the process. If you have a falling end portal and another falling block, then you can make a flying machine that automatically places down a line of that other falling block. The idea is to build a line of end portals, and then use those end portals to place down and dupe a line of the other falling block next to it. So we can make fully automatic block placers. Transporting the falling blocks back to the flying machine might get quite slow after after a few steps. But in the end dimension you can make a linear speed automatic block placer if you additionally use a falling end gateway. At every step you additionally place down an end gateway and use it to link up the new position of the flying machine with a fixed position in the end. And then you can transport all the falling blocks back to the flying machine in constant time. The open problem here is to actually build that.