I think, over time all mixers are going to be shut down by various government entities. Even if they are doing nothing illegitimate, for some reason everybody in law enforcement sees them as illegitimate. I will also say, with more and more exchanges that are not requiring KYC going away I see privacy becoming more and more difficult to obtain.
I have the same sentiments, I think eventually mixing will be portrayed as being synonymous with criminal activity and that false narrative will be pushed out by those that wish to control the agenda. Yes mixers can be used for criminal activity but does not they will. but there might be some sort of radical transformation or implementations which could theoretically keep certain mixers out of trouble but it depends on how law enforcement agencies approach it in conjunction with mixers.
Tinfoil hat paranoia, the last mixer that is left standing is run by the NSA....

Eh, JollyGood is just asking a general question that's probably on the minds of quite a few members here, and as far as criminals using any mixer service....that's similar to the argument that bitcoin or [name your cryptocurrency] is/has been used for illicit purposes and therefore is bad. It's a silly argument against crypto, and if it were valid then fiat should be bad as well as all guns, knives, and anything you can think of that's been the tool of criminals.
It certainly was a general question and that debate is twisted somewhat by those that see me wearing a signature and overlook the question raised. You are right it is a silly argument against crypto but those that are putting out false information on a regular basis by equating criminal activity to crypto are simply hiding ulterior motives. Like fiat can be used for nefarious purposes crypto can be too but that does not mean it is specifically a tool for criminals.
Who knows what the government is going to go after and with what amount of resources? It seems as though all things crypto are under the microscope at the moment but that could change. I do hope there are some powerful bitcoiners with political influence lobbying for us, because the little guys like myself can't really do much of anything to sway those politicians looking to criminalize mixers and whatever else.
If those that have become super-rich because of crypto get together to put forward an alternative view that is being projected against crypto then they could help manage the way crypto is talked about in political circles including the all-important financial departments. If lawmakers get a real understanding of what Bitcoin and other crypto are then they will be far more better placed to make the safest and best decisions.
It is inevitable that most if not all mixers will be used for (or will be attempted to be used by criminals for) nefarious purposes
It is inevitable that most if not all banks have been used by criminals for nefarious activities. How many closures have we had as a result of that? Even when banks engage in scams, they just get a slap on the wrist.
That is true, either they get financial penalties or bad headlines but hardly ever are there criminal cases against banks and when there are there is little to no talk about them being shut down. The problem Sinbad faces is different to competing mixers because none have been accused of being previously associated with Blender and that makes the difference here.
Can I ask a counter question,
Is Whirlwind.money Next To Be Shutdown? 
You can as many questions as you like

If Sinbad is operated by the Blender team but Coinomize, YoMix and Whirlwind (and others) are not, then the chances are the others will last longer than Sinbad.
This is one of the concerns bitcoiners have had so far - and of course I think it's normal and makes sense.
The government will try to put up more of a fight for any mixer and it's definitely on their watch list. Of course their main reason is to prevent a lot of money laundering cases - but actually they seem to have another mission besides fighting crypto, confiscate bitcoin for example.
The same will probably be attributed to some of the other mixers currently growing and developing, but of course it's a matter of time. Until then, I think the government will shut down any mixer service like they have done other mixers before.
I cannot add more to what you wisely posted other than my opinion that all mixers are most probably being watched by various law enforcement agencies and the moment serious criminal activity is detected they will be shutdown.