Modularization aside (and it's terrific to have in the library), what additional functionality are you most excited about with this release?
* New pretty continuous color schemes (viridis, rainbow, ColorBrewer)
* New axes that are easier to use.
* Vastly improved circle-packing layout.
* More stable, extensible force layout.
* Cleaner implementation of immutable selections & transitions.
And a ton of other stuff. Taken overall, it feels like a big step forward in robustness and cleanliness. And I’m hopeful that it’ll be easier for folks to develop more D3 modules.