Both the Republican and Democratic parties currently have favorability ratings that are significantly net negative. There is roughly a fifth of the country that does not hold a favorable view of either of the two parties. That is a serious issue in a two-party political system, and an indication that there need to be chances to produce better accountability, and politicians that better reflect the will of the people.
Imagine if this were a market instead of a political system rigidly designed to enforce two-party politics, and the two major players in the market were viewed so negatively by a large part of the population--you would see them rapidly lose market share to upstart competitors. But that is stopped by the system's anti-competitive design.
Like any smart oligarchy, Democrats and Republicans have managed to slowly cement a mutual protection system into law. In this case, it is election law, including (but not limited to) tough ballot qualification laws and a plurality vote, winner-take-all system. Until the underlying electoral system is changed, I don't think you will see the diversity of choices better match the will of the population. And I don't think you will see real accountability for the major parties. Before you can see relatively permanent and relevant third parties, you first need to create the playing field that makes that possible. Looking all over the world, we see that design of election laws often directly correlates to how many relevant political parties the country has.
Unless we move away from a plurality winner-take-all system and toward instant runoff voting, very quick runoff elections, and/or proportional representation, it is hard to envision how there can be a substantial effort to hold both parties accountable at the same time. Any attempt in the current system will continuously run into the “spoiler” problem.
But this latest poll does seem to indicate there is a hunger for other choices. That could be more progressive candidates, more conservative candidates, or even candidates that may better fit a district's majority opinions but exist outside the traditional left-right paradigm. Socially liberal fiscal conservative libertarian-leaning individuals, or social conservative Christians that also believe in a liberal, strong social safety net.