@freemo Totally agree with all of that, but usually those shifts you're talking about come as the result of war or revolution. And most (all?) such shifts in our country's history were basically just reformations of the previous two powers.
I agree that it won't necessarily be the *same* two powers vying for control, but FPPT does significantly incentivize a field being reduced to two options through coalition building.
But most importantly, a third party would need some kind of serious momentum (usually kicked off by major events) to take the lead, and I just don't see it happening this year.