Fwiw the github page for that proposal isn't linking to what seems to be the most recent discussion *. I thought type-annotations-as-comments was a no-brainer, but it seems messy. The Sept 2023 discussion shows that it is complicated by the current variety of annotation schemes (TypeScript is not the only one), and the parsing subtleties, which gave rise to unresolved questions about what is the basic motivation. bummer.
* https://github.com/tc39/notes/blob/main/meetings/2023-09/sep...