I'll take a shot at this even though I have no connection to vercel or scriptc. I have been working on tsonic.org for a year - which is a transpiler which will let you transpile typescript to rust, c# and mojo instead of javascript.

First, you can't get very far without self-hosting. You'll need many extensions and hooks into the compiler, and those are probably all in TypeScript. You can't use the mainline tsc v6 compiler because it's slow and runs Javascript. scriptc will not be able to compile the v6 compiler into native code either, because that code is too dynamic. And you can't use v7 because it's written in golang.

So the only option is to rewrite it in typescript, and compile it into native code via scriptc itself.

We did exactly the same thing, and it's here: https://github.com/tsoniclang/tsts-legacy

We decided to move away from it, by writing a golang-to-typescript transpiler - https://github.com/tsoniclang/gotots. That produces a working typescript version automatically from Microsoft's v7 compiler, but we just decided to not proceed with that because (a) LLMs have gotten so much better at doing these rewrites, that it's not expensive to maintain a port and (b) looking at signals from Microsoft, they don't seem to be so sure of golang anymore. I suspect it's going to get rewritten in rust.