As a RampTramp of some years' standing, I'd say stick with the headsets and cables and make every pushback at least a two-man job. We've experimented with very well-known Swedish-made cordless headsets (Bluetooth ?) with a view to them eventually replacing the cabled ones as they conked out. The audio quality was lacking, the pilots didn't like them so we stayed with the cabled variety. If it ain't broke...try hand signals.