If your controller is configurable enough, you could assign "bank" and "program" change commands to your pads. This is a way of "changing" the sound for the layers associated to the MIDI channel your controller is talking to.
The new feature we are discussing and implementing is for "loading snapshots", that is a completely "different way" of changing the sounds. A snapshot is a Zynthian's status dump. It's a set of layers, each one associated to a synth engine and MIDI channel, with assigned bank, program and MIDI-CC values. @mheidt has linked the discussion in his answer above.