That's a great point, and being aware of the dangers of shouldComponentUpdate is what this post is all about. There are a lot of gotchas when using PureComponents, and can lead to bugs if you're not careful.
Also, recalculating derived data (building static lists) in render() is very wasteful, and is also another gotcha when using PureComponents (object copying). Removing object copying from render() speeds up the actual render() call and allows you to take full advantage of PureComponents.
We are experimenting with ways to make all of this a bit easier, and hopefully will have some good news to share in Part 2 :)
Also, recalculating derived data (building static lists) in render() is very wasteful, and is also another gotcha when using PureComponents (object copying). Removing object copying from render() speeds up the actual render() call and allows you to take full advantage of PureComponents.
We are experimenting with ways to make all of this a bit easier, and hopefully will have some good news to share in Part 2 :)