Oh, I read a bunch of answer, and I didn't know war existed :/
As I see it, there's no intention of bringing Factorio to multi-threading since it can only benefit to those with big rigs and would make it worse for lower end hardware.
In addition to that, the release is quite stable and optimized (nobody can deny it), and breaking all those optimization into smaller pieces doesn't seem to be worth it.
I know that things like pipes are multi-threaded, thank to a better algorithm and the end of fluid mixing. Same for belts.
Still, I wonder how much percentage of simple entities like inserters or bots can be parallelized...without breaking the current state.