He missed the proposal within the context of the current conversation. He is actually responding to an email earlier in the thread that linked the original email from 2005[0].

RMS does't use an Internet browser so he fetches pages and recieves them in email. He received the html file a day after he had already written his response that he self quotes[1].

He wrote the linked email before he replied without actually having viewed the link of the 2005 email. Therefore, he was unaware of its contents.

It makes little sense out of context.

[0] https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00...

[1] https://lists.gnu.org/archive/html/emacs-devel/2015-02/msg00...