Old Farts have been doing this in doubles for decades. Difference is they do it against 40-60 mph serves. Fed is doing it against 80-90 mph serves...
Yeah, I was doing it every once in a while even before I became an old fart. But, as you say, those were very predictable and very attackable 2nd serves. Impressive to see Roger doing this against ATP servers. Some of the servers he's used it against were guys that often hit 2nd serves in
excess of 105 mph. He employed the SABR against big serving, Kevin Anderson (at Cincy), and Leonardo Mayer (USO).
He also stepped in & attacked some of the 2nd serves of Fernando Lopez (Cincy), another guy who can hit monster serves. (Not certain, however, if he employed any full-fledged SABRs against Lopez. Had heard that he did but not seen any vids that showed it). In the following video, from his final against Novak in Cincy, he SABRs 2 serves that were clocked at
106 mph.
When asked if he would employ SABR against Isner, Fed indicated that he did not plan to do so. He indicated that he hasn't played often enough against John's huge serves to get a good read on them. He mentioned that he was better at reading big servers like Roddick, Raonic and Karlovic.
http://www.tennis-x.com/xblog/2015-09-06/20598.php
... I am sure Becker has instructed Novak to put the first SABR return right through Fed's belly if he tries it in the finals.
Easier said than done. Roger takes the ball so early that he gets the serve back to the server (so quickly) that they are sometimes still recovering from their own service motion. Roger hits many of those SABRs quite deep. Of the 11 times (or more?) that Roger used it in the final at Cincy, Novak only managed to hit 2 decent replies -- 1 passing shot and a good defensive reply (followed by a great lob). Roger failed on to make his SABR on 2 of those 11 attempts.
Given that he had 9 opportunities to return Roger's SABR in that final, Novak might have been tempted to blast a reply back at him -- IF he was in position to do so. Difficult to blast Roger at the net if you are near the baseline and just recovering from your serve.