News is emerging that the government is not trying to compel Apple to unlock just one iPhone from one terror suspect but has at least a dozen other cases ongoing in which it wants to coerce Apple's cooperation. I haven't looked at any news archive but I'm pretty sure there haven't been 12 terror cases in the US recently. This leads me to further my belief that the DOJ picked the San Bernadino case because they thought it would make them look the best and Apple look the worst.
You can imagine the difference in reaction if, say, the government went to court complaining that it couldn't unlock the phone of some dude who's been running cigarettes up the east coast avoiding paying taxes on them. Same technology, same principles, but I expect many more people would laugh at the government's position there.
So on the one hand, this really is the security theater version of things. On the other hand, the security state's nightmare future has already arrived. Life is about to get rather interesting, I think.
Previously I scoffed at the idea that this case could land before SCOTUS. I am now changing my mind - what the government wants to do is apply a nineteenth-century law to a twenty-first-century problem and I expect these cases are widely enough spread out that we'll see different circuit opinions on that application. Those two factors make it much more likely SCOTUS would take up this case, though that seems unlikely to happen before 2017 or more likely 2018.
That's both good and bad - this country has always had an uneasy relationship with the notion that private third parties can be forced to intercede on behalf of the government in carrying out law enforcement activities. I imagine the late Justice Scalia would have had some sharp words to say on this matter and I can't intuit how the current 8 would vote on this matter. The way the question is framed will, I think, have a much bigger impact than the particular subject matter of the case.