That is exactly what one of my friends was telling me last week-end. He said the fact that all these terrorist organizations (Al Qaeda included) never attacked Israel or Saudi Arabia is a clear indicator that the U.S. is somehow pulling the strings again. It seems far fetched, but who knows...
Honestly, the one thing that is interesting about ISIS is that they are extremely smart and are playing their hand really well. They are very intelligent on how they conduct warfare. It's a relatively small group of soldiers (what, they are up to 30/40,000 soldiers now) conducting lightning strike quick attacks.
They are going for territory right now and anyone and everyone AGAINST them is immediately put to death. This means in their 'cleansed' territories they have no more opposition of any kind. NONE.
With their captured territories they are selling oil from the captured fields and are amassing great amount of wealth which they then reinvest to pay their Army of goons. Large swaths of people in the middle east are poor and unemployed and are now being 'rewarded' and paid handsomely. At the same time they can have/use whatever they want.
Playing their cards smart politically. Negotiating with the Turks (trading hostages) and playing the Assad card, playing the Russians against the U.S. using the Assad card etc. etc. etc.. My best guess is that once they have Iraq and Syria they will be quiet for a little while. Gain strength, build alliances etc..
They are currently not in any shape to take on an actual 'military' force. Take on the Israelis would be suicide for them - besides the fact that they actually have to physically go through Lebanon first. Attack Turkey - they get NATO involved. Attack the Saudis the U.S./world gets involved pronto and as a country its WAY to big (for now). Threatening the Saudi oil fields would piss EVERYONE off world wide. Might even get the Russians pissed off enough. Also, my guess is to many 'rich' Saudis are secretly supporting them.
Because its ONLY Syria which was a cluster before and 'Iraq' where everyone wants to avoid another 'war' they can pretty much do as they please. They have a relatively weak U.S. President that likes to hold pretty speeches but is a little short on action (Come on, Dude can not even get his own Secret Service detail straightened out). 15 air strikes over several days to 'help' the Kurds so ISIS can't take Kobani? History repeats itself and the Kurds are giving the shaft (They don't learn - do they?).
So what is next? Which countries would be 'easy' pickings? My guess is Libya, MAYBE Egypt (military is to strong in that country though to let that happen). Lebanon would be an option and could be another stepping stone.
Israel and Saudi? Not going to happen for a 'while'!