Hi Alex (I have an email from you that I have to respond to)! TS guy here. We've had discussions around this and the reason we use our own AST format is for compilation speed and editing scenarios, both of which our team really focuses on.

I'll also note that incredible folks like James Henry have already written tools to convert TypeScript ASTs to the ESTree format[1]. I've heard it's been working well for using ESLint on TypeScript code.

[1]: https://github.com/eslint/typescript-eslint-parser