Ah, this is part of the Turbo project that had the whole controversy earlier this month around DHH unilaterally removing TypeScript, citing only his own experience, despite overwhelming community disapproval: https://github.com/hotwired/turbo/pull/971 It's a really cool pattern to have server-side rendering drive a specification that's used by web and native components alike. Airbnb uses this pattern to great effect:…
Turbo is free and open-source. Nothing stops people from forking and keeping TypeScript alive in the fork.