Part of the case study series.
About worldbuilding? I would say yes, because whether or not this is possible is the key to the premise of my world (an artificial star). It is certainly strongly based in science, but I think that's okay. After all, I want my world to be believable.
Risking off-topic? I would say not. It's broad-ish, but a lot of the answers said that it wasn't possible, for various reasons, so maybe it's straightforward.
About worldbuilding? Yes, as it defines tactics in a conflict that will impact the entire world (in this case, one nation).
Risking off-topic? Possibly too broad, and it does focus on the actions of individuals - and there are a lot of possibilities, as evidenced by all the answers it got. So maybe this one's closeable.
About worldbuilding? Yes; the actions of this person will shape the fate of the entire world.
Risking off-topic? Well, it's currently closed, and one of the close voters was me. I think it's really too broad as it stands; there are loads of possibilities.
About worldbuilding? Heck yes.
Risking off-topic? Again, this one could be too broad, but it's broader than most worldbuilding-process questions, in my opinion. I think it's fine.
About worldbuilding? Yes.
Risking off-topic? It's similar to a What-if? question, but it does set guidelines and explain what I've considered, as well as the background. It also focuses only on small part of my world.