I'm somewhat skeptical of the thought that FPTP makes it harder to rig the system. I'm probably a bit information diet biased here, but it seems (as an example) that Republicans have had more court rulings against them due to unfair gerrymandering of districts. It seems who holds the power gets to determine the districts, which would help preserve power. If there wasn't a two way swing, it would arguably be harder to gerrymander in one parties favor, as it _should_ be more difficult to hold 51%+ power if more than 2 parties are available.

How cool would it be if we passed gerrymandering restrictions based on the fractal dimension of the district maps :-)

Wouldn't you expect even more frequent regime changes in a system where the vote was split between three or more parties? This is a common criticism of minority government.

No, only if the electoral system is winner take all. Multiparty proportional systems can be very stable,for example, Germany 2000-present