You shouldn't have any trouble with Xenoblade Chronicles (other than the fact that you'll get stuck into the game for hours... and hours...) This game actually isn't all that demanding CPU wise, but it seems to like being demanding on the GPU a bit in places. Again, your GPU will be up to the task.
As for additional multi-threading opportunities in Dolphin, while there are a handful of areas that may be looked into in the future, I would not expect any significant breakthroughs any time soon (or at all?). Emulation of the GC/Wii hardware is a very linear task (calculations must be done serially, in order for the most part) with only a few places where processing can be done in parallel. The FAQ explains this in depth: https://dolphin-emu.org/docs/faq/#couldnt-dolphin-use-more-my-cpu-cores-go-faster
As for additional multi-threading opportunities in Dolphin, while there are a handful of areas that may be looked into in the future, I would not expect any significant breakthroughs any time soon (or at all?). Emulation of the GC/Wii hardware is a very linear task (calculations must be done serially, in order for the most part) with only a few places where processing can be done in parallel. The FAQ explains this in depth: https://dolphin-emu.org/docs/faq/#couldnt-dolphin-use-more-my-cpu-cores-go-faster