The Dem leadership is actively supporting Bernie Sanders to run for Senate in Vermont.
You've got folks ranging from Barbara Lee to Jose Serrano to Dennis Kusinich around the House caucus.
And Nancy Pelosi, while not a radical, is still probably the most progressive House Dem leader in the 20th century.
There may be less radical proposals kicking around, but that I think reflects realism about the realm of the possible, since you can't even get a vote on pretty moderate proposals these days.
So the problem returns to numbers and control of the chambers. Expand the numbers and new openings for radical votes would appear.
Nathan