I think a performance improvement in anything existing is great. Especially for something as big as TSC. It has such a large amount of usage that many people will appreciate. While it would be great to have it reimplemented effectively in something inherently faster, not improving what we have while it's clearly still the best option wouldn't be helpful.
> TL;DR: The TypeScript compiler is now implemented internally with modules, not namespaces. The compiler is now 10-25% faster. tsc is now 30% faster to start. Our npm package is now 43% smaller. More improvements are in the works.