If you had a rotating mechanism which allows slip then you could have rotor shafts which rotate all the blocks in a column while braking mechanisms prevent all the blocks in a given row from moving. Or you could have both rotor rows and rotor columns if you implement a rough mechanical equivalent of the hysteresis systems of ferrite-core memory. Or (I think GistNoesis suggested something similar https://news.ycombinator.com/item?id=44794092 ) if you hide a neodymium permanent magnet just under one corner of each of the blocks you could use a pair of electromagnets behind that block to pull the block from either orientation into the other, almost a solid-state solution apart from the axle the block would rotate on and potentially one which could set the entire display at once.