Advertisers and tracking services will fight this to the bitter end.
....and if this is ratified as a web standard, governments could simply enforce honoring such headers by law. In Norway, a national register has been in place for years where registered citizens opt-out from fax and voice spam. Norway also have laws which prevents advertisers from filling your (physical) mailbox with junk (you just place a sticker on your mailbox).
Well actually Web browsing and e-mail can/will gain an advantage; Web browsers and e-mail clients do cache a lot of information. Also the trend these days is to move indexing from server to client (desktop search).
If builders built buildings the way programmers wrote programs, then the first woodpecker to come along would destroy civilization.