I'm not trying to be fatalist or defeatist, but honestly, all you can do with that is change which parties the top 2 contenders are in, you can't prevent there being a top 2 contenders, or it being in every individuals (whether candidate or voter) self-interest to align themselves with one of those two. Even the most diverse party systems in other countries always come down the faction in power against the opposition faction.

There are only two ways of changing this, and neither of them is ranked voting, instant runoffs, open primaries, or any other alternate electoral mechanics. The first way is to change reality so that laws do not either exist or not exist, and bills do not either pass or fail, requiring legislators to vote either yea or nay. That is not possible physically, but philosophically we can still consider it as if it weren't a necessary, logical, and metaphysical certainty.

The second way is to change our understanding of reality, without needing to change the electoral process at all. The truth is that it doesn't matter how government representatives are selected, some of the people being governed are going to have wanted a different representative. It is inherent in the duties of a government official to serve everyone, including people who voted against them (or didn't vote at all). If an official got 12% of the vote (while running against a dozen others who each got less) or 88% of the vote, it shouldn't matter, and the responsibility of a citizen in a democracy is to consider the official legitimate regardless. This is difficult to do, I realize, given that we must judge the validity of a government (particularly a democratic republic) by the results as much as the system itself. Most people want everything to be simple, and it isn't surprising that many don't believe that an office holder who only got a plurality rather than the majority of the votes deserves to be in office. And so it isn't surprising that office holders (regardless of party, but more often authoritarians) consider their selection as a mandate to serve their Party's unified goals rather than their constituent's diverse interests. Logic makes the first easy and the second impossible, so why would anyone bother not doing the first or even attempting the second?

Even an official who got 88% of the vote must be fair, and adequately represent (not faithfully parrot, but decently serve) the other 12%, and anyone who abstained or was disenfranchised. We rightfully have no tolerance (though we are not everyone in this case) for using government power once secured to punish those who didn't help secure it or pledge to help maintain it. But logic makes us animals or robots: to be fully human, we must accept the need to attempt potentially impossible tasks, and that includes self-government, which is the real purpose of both republics and democracies, either separately or in combination.

We can either abandon that pretense of "the problem is the 2 party system", which is a strawman, and recognize that a plurality is just as legitimate as a majority, so we no longer demand (by our expectations, whether or not we demand it in our actions or words) that we maintain a two party system so that whoever gets more votes also gets a majority of votes; or we can insist it is a fact rather than a pretense, and say that unless an unlimited number of candidates are on the ballot and one of them gets a majority, no election occurred, and get rid of parties all together. I know which one I think is more achievable and productive; how about you?