The problem is as it has always been. Trying to put people first inside an economic operating system that puts only profits first, and is already teetering on a combination of its own internal contradictions, as well as the further complications of decades of reform effort that have left it a much more complicated form of itself, is an exercise in "doing the same thing over and over again, and expecting different results." Sure, the reforms have provided people with some relief, but it has mainly served to make the system itself less manageable overall, and a very great deal more difficult to try to reform any further.
When are people on the left, whether still close to the middle or not, going to accept the fact that Capitalism is what it is. And as such, you can only screw with it to a certain degree before you start to make things even more difficult than they already were.
The problem isn't how to reform it to be humanly acceptable, it is to realize that it has had its day and that it is way past time time to start over. And it is time to do that precisely because new technology has made it an absurdity. An absurdity that goes beyond the fact of its almost guaranteed proclivity for inequality of outcomes, and a structural inability to handle holistic thinking (which is a big part of why prices hardly ever reflect true costs).
This is the one and only challenge for the left now and the sooner they realize it the better. It doesn't matter if it is Bernie Sanders, or someone a little more towards the center than Bernie. Even if you could pass true Socialist reforms on it, you would only make it weaker than it already is; most especially now that global competition is only getting worse. That's just the way it is.
The Fourth Industrial Revolution could bring mass global unemployment.