Tullio Campagnolo's 1949 patent describes the Campagnolo Paris-Roubaix derailleur system. This had a single lever that both loosened (and tightened) the rear wheel's quick release and shifted the chain. However the chain shifting device operates on the top run of the chain - requiring the rider to pedal backwards while shifting.
This, 1948, patent describes a prototype of the Campagnolo Paris-Roubaix which has the chain shifting device operating on the lower run of the chain. Frank Berto is unimpressed by this idea, claiming that any hang-up during shifting could cause the wheel to be shot out of the front of the dropout.