This release makes Dimple compatible - and reliant upon - D3 version 4.3. I have not marked this as a major version change because any charts using just dimple functionality should continue to work as before, however this is a slightly grey area, as most advanced implementations of dimple charts are likely to also use D3 functionality and may well run into one of its breaking changes.
Therefore I would only recommend migrating existing work to this new version if you have reason to move to the latest d3 release.