There is no obvious explanation for why you would want this anywhere I can find... Does anyone understand? If you wanted this, wouldn't it make more sense to extend the last version of TypeScript before ts-go instead? Hmm.
I guess the question is why you wouldn't use TypeScript 6 as the basis for that.
Stage 1 to writing a bootstrap able language is using the intermediate step of compiling it with a compiler written in another language so that you can write a compiler for yours. I’m sure they did this in order to get a binary of the first self-compilable version.
All the twitter types are busy rewriting typescript to speed it up, just because they can. It's becoming a meme.