IMHO it's extremely implausible that jihadi chatter in open forums would cease because of an impending attack. There are just too many wannabes who would keep posting even if the real actors drop out for a bit. And the absence of any one (or even several) posters can be due to lots of other causes - machine problems, personal problems, etc - that have nothing to do with attacks.
The other thing that occurs to me is that there are reasons why EOM and others might "disappear" for a while even if there isn't an attack. Remember that it is the hajj, and the Eid. He/they may be preoccupied with very mundane things associated with these events and want us to think that they're off on some big mission - it makes them feel important and strikes fear in their opponents.
If there are some viruses or other cyber attacks ongoing, that could easily explain several sites going quiet; these things can affect many server systems just as much as end-user PC's.
We shall see shortly. I wouldn't pre-judge but it does seem "interesting." FWIW in some of the things connected with my "day job" we've been having lots of perfectly mundane issues with domain registrars etc for almost a month and a half now (!!!). So there are some areas on the Internet that have been rather, shall we say, discombobulated lately in ways that have nothing to do with the jihadis.