The problem you have is the demographics you describe also have opinions on the things you claim a progressive platform (that enjoys popular support) can be built on.
Not to mention that capitalism is frequently criticised as a factor in the problems (to be solved you list) by leftists. I'm not here to turn the thread into a thread about capitalism, I'm just pointing out the correlation made.
You definitely don't want a progressive leftist, and maybe not a leftist at all. That last one's kind of a semantic hole to go down, so let's just stick to not wanting a progressive

Progressive healthcare alone (or anything approximating it) gets gutted on sight. If the Democrats as existing in the current power structure cannot get through bills as they'd like, what hope does any realistic progressive platform have?
Leftists frequently get told to be realistic. We have done many times in this thread alone. I'm not sure your suggestion is realistic enough to be feasible. Though I'm sure that doesn't stop individuals, or even small groups, from trying, nor would I want folks to. But as a platform? I'd be interested in seeing how you see that coming to be.