Wouldn't that conflict with possible future optional static typing? It's only Stage 1. I'm hoping it doesn't make it in its current form. Some good discussion in the issues, though: https://github.com/tc39/proposal-type-annotations/issues
It would be hard to separate ignored ones from ones that would use a possible future optional static typing system. They would possibly have to use a different, uglier syntax.
I'm not sure I follow. Both proposals are suggesting that browser's engines ignore the syntax completely to allow some other, external, process to check them.
They use slightly different wording but are describing the same basic idea: This syntax will be ignored entirely and then optional/other process can use this area for whatever.