I agree 100000% on the Videos icon. It's a relic: when every Mac user was a pro video-maker using video-editing tools every day, I guess it made sense to keep it consistent. I don't come from that background, so that icon never felt natural; I agree that a "Play button" would be so much better.
The idea of making icons dynamic is great and would go some way towards compensating for the lack of real-time home-screen apps. Newsstand proves that it can be done, and Apple should probably use it a bit more, battery be damned. There is a risk in opening such an API to third parties, that developers will start blinkifying their icons to jump at you, transforming one's home screen in a giant flashy billboard; but it would certainly be a nice touch for homegrown system icons.