Apparently, I am in the vast minority, but I’ve been doing heavy animation in web apps, mobile web apps and with Ember for years. Here’s an example Ember app with heavy animation: http://migration.nikefuelstream.com/stream/bridge-the-gap
Animations should be controlled by Javascript and backed by requestAnimationFrame for maximum control and performance. I’ve written more of my strategy online (How Do I: Animate « Thomas Reynolds).
I believe Ember.js should adapt an existing Tween engine, such as Tween.js to be promises based. Tween & timelines (sequences of tweens) should be treated similarly to ajax and be able to delay route & state transitions until they have completed.
The limitations of a system where you cannot sequence transitions is huge. We should develop a robust system, not the lowest-common-denominator of “crossfading views”. If animation were baked into Ember in a robust way, it could be used to control image sequences, run illustrated animations, respond to touch/mouse events and respond to scrolling for ye olde parallax.
Thanks for reading.