Currently the active preset can be selected using mouse or keyboard.
But there is no way to use this function in a mouse and keyboard free live situation, because the selection box is not assignable to a MIDI controller.
I'm right aware of the device chain solution which is fine in some cases but there is one major drawback:
Every instance of a plugin, even when it's not processing any audio and the user interface is not visible, does consume a bit of RAM. Depending on the plugin and the number of presets used this can add up really fast.
Therefor I think preset change via MIDI would nicely complement the device chain solution and would also help with some of the instrument plugins which don't accept program change messages but can do preset changes through the host.