Comes out of the same tradition of Marxist thought that you are saying is unrealistic, right ?
Eugene Debs, the man many people see as the father of Democratic Socialism in the United Sates was himself a Marxist. One need not be a Communist in order to be a Marxist. As all Marxism is, when not treated like a sacred cow, is simply a form of critical analysis.
As to not being Progressive, well if you mean not Liberal than I suppose in that sense yes it's not. But neither is Democratic Socialism sense both seek to eventually end capitalism. The Liberalism that we've seen associated with the Democratic Party since The New Deal does not seek to end capitalism but rather reform enough to make the system bearable for the majority of the population.
Now if you mean Progressive in the sense of social progression than I think we can say Communism is Progressive as it advocates an Egalitarian Society where The State has withered away and the Societal Structures that made the power dynamic of capitalism possible no longer exist.
Personally though, I think a strong Labor Party would go a lot farther in dismantling Capitalism than either the Legislative Reformism of Democratic Socialism or The Revolution that Communism advocates.
I think history has shown that it has been The Union that has been the most effective weapon for American Workers in fighting the class war. Either way though if capitalism isn't stopped our Future I think will be somewhat more deprived than we'd like it to be.