(You could replace FPTP with STV to keep the districts that elect representatives in the house intact.)

I'll start.

The Democratic party breaks up into the neoliberal and progressive parties.

The neoliberal party is where centrist candidates like Joe Biden and Michael Bloomberg go.

The progressive party is where progressive candidates like Bernie Sanders and Elizabeth Warren go.

The Republican party might lose a large part of their electorate to the libertarians, since many Republicans are more concerned about letting business prevail and don't really want cultural conservatism.

Andrew yang maybe also leaves the Democrats and founds his own party, the party for online reform.

The greens also become significantly more popular but they may have too much in common with the progressives.

The Senate could be changed to include as many seats as the house for proper representation.