So, as I thought, this does not come from any official IFAB document - just from an unofficial and unattributed 'off-the-cuff' interview by an unnamed IFAB official. I'm confused by a number of things in this report. It talks about ideas to increase the amount of actual playing time in matches and says they are, "Looking at ways to cut down on time-wasting, speed up the game and increase playing time." This echoes almost exactly word-for-word, phrases used on the IFAB 'fair play' website. This site, as I understand it, lists all the ideas currently and officially under consideration or merely discussion, in relation to improving the game in several significant areas including time-wasting. Several of the ideas mentioned (substitutes being required to leave by the nearest boundary, allowing defenders to play the ball inside the penalty area after a goal kick or free kick etc) are indeed listed on that site. However banning substitutes in added-on time is not there.
Also the 30 second thing, although it's something I've heard of and which some referees apparently use as a rough 'rule of thumb' is not a 'recognised formula' as far as I'm concerned and is wholly unsupported in Law. The law says that, "Allowance is made by the referee in each half for all time lost," (emphasis mine) not just some arbitrary amount that may or may not reflect the actual time lost. If a substitution takes 30 seconds, by all means make allowance for that amount. However if it takes more (or less) time then that is the time, according to the law, the referee should make allowance for.