How rewriting something internally makes Racket not mature? Sounds like refactoring to me and with an extensive test suite there's nothing to be hysterical about.

Maybe I just have a different working definition of these words. To me "mature" means "fully developed" and "polished" means "achieved a high level of refinement". Rewriting it all to introduce a major feature that fills in a longstanding hole in the language doesn't say "mature and polished" to me. Because often times many bugs are introduced into a codebase on a major rewrite despite extensive test suites. Typically people might prefer a mature codebase to one that's just been rewritten precisely because it hasn't been vetted over years. "mature rewrite" sounds like an oxymoron to me, and I guess no one else agrees but I find it strange. That is all.