I am sorry to bring this up again.

deterministic multithreading is a pain but fortunatelly I enjoy the suffering of parallel computing :-D.

I think we have to differentiate 2 Problems:
self containing threads and world interacting threads.

self containing threads (easy):
As boskid mentioned there ...

Well, i have 2 ideas.
It would be great to have the possibility to programm. A ingame microcontroller that works on user specified programms. Or a REST Interface for an external application.

another idea would be imgerium galactica 2 related.
Start on a planet, build up your economy, launch ...