I don't think asking xf86-input-synaptics to listen to unrelated events is a good idea. However, there is functionality already present in synaptics that we may be able to use: the "Synaptics Off" option. Syndaemon already uses this to disable the trackpad when the user is typing on the keyboard. We could add functionality to syndaemon to listen for lid closure as well.
I don't think asking xf86-input- synaptics to listen to unrelated events is a good idea. However, there is functionality already present in synaptics that we may be able to use: the "Synaptics Off" option. Syndaemon already uses this to disable the trackpad when the user is typing on the keyboard. We could add functionality to syndaemon to listen for lid closure as well.