Comment by paxys
"Native typescript execution" can mean two different things:
1. Chrome/v8 takes TS code, compiles it down to JS internally, erases types, and then runs it like normal. This isn't going to be too hard to do, but also isn't going to be very meaningful. Compiling is a one-step process in any case, and plenty of tooling exists to make it seamless.
2. Chrome/v8 actually understands TS types at runtime, and throws exceptions for mismatches. This isn't going to be possible without a major rewrite of the v8 engine and the ECMAScript spec itself.
And a big challenge for both of these is that TypeScript is iterating at too fast a pace for something like Chrome to keep up. It's best to just leave versioning and compilation for the developer to manage and give end users a consistent JavaScript experience.
I think there's also option 3, v8 understands types and uses them for optimization, but handles wrong types gracefully.
I don't think any type of understanding TS would require changing ECMAScript spec. Would a TypeScript-understanding parser not be able to handle normal ECMAScript correctly? It could switch between two modes based on the file type.
For option 1 the speed of TS development is not an issue, as Chrome would only need to include some up-to-date compiler, and the TS files could specify their TS version. But doing TS compilation in the browser would only be a small nice thing for devs, for website users it would be a downgrade, as the page load would be slower because of the compiling and the larger file sizes (JS files can already be very big these days).