Can you explain why the two proposals would "conflict?" Seems like they're proposing the same thing to me.

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.

There are other languages that have optional static typing that don't treat types as comments. JavaScript could evolve to add support for this.