Well, for one, there is the implication that Cohen made that Trump personally directed him to commit a crime, and it has nothing to do with the Mueller probe which would make it look less political than connecting it to the Mueller probe would be.
I wouldn't say it makes it more likely, there are plenty of reasons they can use already, but being able to connect Trump to an actual crime does give them a bit of a political escape route.
Theres still the second Manafort trial (unless Manafort caves before that), however many shoes left to drop from the Mueller probe, and the Mueller probe report itself (they'd better make it public, I think I've read that Mueller intends and wants to make it public when he does release it). Cohen's lawyer has also hinted that Cohen has stuff that Mueller would be interested in and has said that Cohen would be willing to talk to Congress without immunity.
So, there is so much more still left to drop.
I think it stems from Cohen saying he had things on Trump that he was willing to tell Mueller. We know absolutely nothing about what any of that is, but it could be more about the Trump Tower meeting that could lead to something that could lead to something else that could lead to impeachment. If the Democrats retake enough of Congress, anyway, since it won't happen as long as it's controlled by Republicans.
Somewhat ninja'd. Good point on retaking Congress because even if the Democrats somehow manage to get into the majority in the Senate, they'd still have to get 2/3ds vote in the Senate, which means convincing some Republicans.