Instead, is Orbiter going to become multi-core anytime soon? Maybe next version?
There is one big advantage: increase of stability of the physical engine, which could be refreshed more frequently than the graphical one then. Measurable effect - possibility of greater time compression and increased stability in the atmosphere under more than 10x TACC. This would require that not every frame is passed to the graphical engine and that a double or even triple buffer of physical engine's "snapshots" is kept to avoid race conditions with the graphical engine. All can be done on the design level, with the addons being agnostic about it.