These exist, usually an off the shelf through-wall AC unit with custom built sleeve and legs. You can see them (or not see them) in some of the landmark pre-war buildings with strict facade rules.
Thanks. Today I learned that window ACs and wall ACs are different things even though they look extremely similar.
For anyone reading this, presumably because windows are thin and walls are thick, window ACs are expected to stick out and thus have vents on the sides, whereas wall ACs have vents only on the back surface.
So as long as you figure out drainage (so condensation doesn't just land on the windowsill), you can install a wall AC in a window and have it not protrude.
