I agree. That is the situation at the moment.
But I think IS and its affiliates (if it has any, they seem quite content to alienate everyone) are trying very hard to polarize the world. And it's not clear to me that every other Muslim will ostracize them.
Go to any mosque and I can guarantee you that people will tell you that ISIS is not Islamic. Also take into account that there are Muslims that are actually fighting ISIS at this very moment. If by ostracise you mean every Muslim has to take a gun and go fight ISIS, then yes, very few Muslims will do that, because many of them fear for their lives like any other human being. But without a doubt, most Muslims isolate themselves from ISIS as much as possible.
20,000* foreigners , it's estimated, from all over have already joined them in Iraq. That's quite a lot of people and is just the tip of the iceberg of potential, and actual, supporters.
I bet that most of these foreigners entered the conflict back in the summer, well before they started beheading journalists, mutilating bodies and making slaves.
Remember, the intention of many Muslims who left to fight in Syria during that time was that they would be fighting to get rid of Assad's regime, seeing that it was tyranny. ISIS at that time was seen as the most efficient group in fighting Assad's regime. That was what made Muslims receptive to ISIS.
Now seeing that ISIS is as brutal, if not worse than Assad's regime, there are very few Muslims who want to join them. ISIS now only manages to recruit individuals who were deeply ostrasized by their community to begin with, and have various issues.
In fact, there are foreign recruits now seeking to leave or are refusing to do what their command asks as they see those commands as not Islamic. So they get killed. Here's a news article about that:
http://www.dailystar.com.lb/News/Mi...ted-100-foreigners-trying-to-quit-report.ashx
As well, many are defecting to other rebel groups or fleeing to Turkey, seeing that ISIS does not treat them as brothers and would rather have them strap a bomb and die instead:
http://www.independent.co.uk/news/w...turkey-or-rival-militant-groups-10034138.html
So again, I doubt that ISIS has much support now from the Muslim Community.