I dont think FD will ever make massive events like supernovas happen. Think of what it SHOULD mean; You see the star explode. Then supercruise away 60 lightseconds, and see it again after a minute. The game isn't built around visible light going at lightspeed. Think of your targets in supercruise. If they are 200 lightseconds away, and the physics are correct, you should see them as they where about three minutes ago. But you see them as they are at that moment.
Also, the background starfield is a still image of the galaxy rendered from the system point of view (which renders during the jump). Sure, a supernova happens slowly by our time standards, but you will never see an animated background in ED.
But sure, if ED lightspeed is infinate, it could happen. But I doubt it.
Yep, supercruise does some handwavium and gives us the newtonian continuum, where changes are observable immediately no matter the distance. You do make some good points on the difficulty of doing a supernova in the game though - perhaps FD can come up with something for it - but obviously there are far more important things for them to be doing first.