The US needs to break the two-party system so minor parties and independents actually have a chance at representation.

Of course there’s no incentive for the establishment to do that. Is there any way for new candidates to run with the major parties, but on a platform to introduce preferential voting when they have the numbers? I don’t know much about factions within US parties, but they certainly exist in my country, and can transform parties quickly if they think they have election-winning appeal.

It would have to happen bottom-up, as you say, so people can get comfortable with such a big change. Also, people are much more likely to elect independents at a local level.