There's still a very long time until 2016 Democratic presidential primaries and caucuses, yet EMILY's List, a front group that supports pro-choice, female Democratic candidates for public office, is now trying to recruit a pro-choice, female Democratic presidential candidate as part of their "Madam President" project.
Interestingly, despite Hillary Clinton having overwhelming leads over all potential primary challengers in recent polling, EMILY's List has already named several other potential pro-choice female Democratic presidential candidates. They've named Senator Amy Klobuchar of Minnesota, Senator Kirsten Gillibrand of New York, Former Governor Christine Gregoire of Washington, Health and Human Services Secretary Kathleen Sebelius, and Homeland Security Secretary Janet Napolitano as potential presidential candidates that they would be willing to support.
The fact that EMILY's List has even mentioned several potential "not-Hillary" candidates would suggest to me that they think there's enough of a chance that Hillary won't run for President that they've already begun their "backup effort" in the event that Hillary decides not to mount a presidential bid.
Of the "not-Hillary" candidates that EMILY's List has mentioned, none of them are what I would call progressive. Gregoire would probably be the most likely of those to run for President, as she doesn't currently hold any elected or appointed office but is a former governor. Klobuchar seems like too much of a backbencher to be a serious presidential candidate, Gillibrand is a political operator (voted like a corporate Democrat when she was in the House and only started voting more like a progressive Democrat when she was appointed to Hillary's Senate seat), and Sebelius and Napolitano are both former governors of conservative states, so they're probably not all that liberal.