The Iwatch has a vibrator with multiple frequencies. I would sugest to only use that function as an advanced "stick shaker" so if SD gives a message on your screen the Iwatch will vibrate acordingly. Messages with a low frequency and warnings with a high.
I suppose non of use have a link between the Device that runs SD and the onboard audio-system and this makes it an perfect solution

I was wondering if you guys would see any use in having the Apple Watch in the cockpit (while being connected to SkyDemon, off course).

'Alerts/Warnings' or 'Time/Distance to next waypoint' seem useful.
Or a reminder to close your flight plan.
Remaining fuel, maybe?

D.