In fact if I recall correctly Google also experimented a couple years ago with a "email signup" field in search ads, but that doesn't seem to have gone anywhere

In fact if I recall correctly Google also experimented a couple years ago with a "email signup" field in search ads, but that doesn't seem to have gone anywhere. Not that it is surprising because if you are searching for something, would you really "interact" with it before clicking the link? Save for a few exceptions, like Google Now-ish results (i.e. information), it doesn't make sense.