Evan You writes up lessons learned from rewriting the next major version of Vue.js.

Two key considerations led us to the new major version (and rewrite) of Vue: First, the general availability of new JavaScript language features in mainstream browsers. Second, design and architectural issues in the current codebase that had been exposed over time.

I found the section on overcoming the bottleneck of the Virtual DOM (and decreasing CPU time by up to 90%) fascinating. ASTs FTW once again!