I agree, and these are two of the main reason we're interested in React. We've had in-house code doing some similar things for a long time, more the batching than rAF in our case, but for much the same reasons. Now that mainstream libraries are offering similar tools and with reasonable trade-offs in terms of functionality offered versus level of dependency, there's not much reason to maintain our own in the next generation of the UI.

In case you're interested, our model code also presents its interface in the form of immutable data structures, with quite fine-grained events available to monitor quite specific parts. But even with that, in something like our small multiples test case, where we're plotting a number of interactive SVG charts using modestly derived data but thousands of underlying data points, it appears that the indirections and tests do still add up to a noticeable level of overhead. Of course that's more demanding than what a lot of web apps will ever need, and our conclusions for our project won't necessarily be anyone else's conclusions for theirs.