No. Due to the game theory of the (non-parliamentary, winner-take-all) system, 2 is an equilibrium for number of parties. As in, smaller third parties are quickly “absorbed” into one of the two large parties to have any shot at winning.

As a consequence, the two parties are constantly changing, to the point that, for instance, the Republican Party of 2024 has little to do with the Republican Party of a decade ago.

Non-American answer: that will never happen unless both parties agree to switch to ranked-choice single-transferrable-vote. So no, never.

The parties don't have to agree. The states set the voting rules and can do so by referenda