It might be proven to be more performant, as it's relying on React's virtual DOM...

adamwong246 on July 18, 2016 | parent | context | favorite | on: D4 – Declarative Data-Driven Documents

It might be proven to be more performant, as it's relying on React's virtual DOM rather than d3's presumably made-from-scratch data binding. Would love to see some benchmarks though.