I would like to have subtitles without downloading a program. Just
like annotations, I would like to make my subtitles on YouTube in my
language and for Google Translate (every single thing on YouTube is
Google now) to translate it automatically into all available
languages.

That would encourage users to add subtitles.
Also I would like to open up the list of available subtitles for that
video using an annotation with "CC" text. Not everyone would know to
click the arrow and then click CC. Linking to the menu would be
awesome.