I can give an answer, but its not going to be satisfactory.
1. instead of Demanding a working mod to be there right now made by someone else, you could also attempt to read the documentation and try to learn it yourself. in the Official Besiege Discord, a special channel is dedicated to modding this game. there are plenty people willing to help you to build YOUR mod.
2. I am pretty sure a couple guys have read your thread but just decided to not answer it simply because of your tone and the fact that they do not know how or just dont see the potential in your idea. Especially since your initial post did not make it clear if you are looking for a mod or a permanent game feature.
3. you could also just develop a special projectile with a massive amount of power using small bombs or rockets. as you know, rockets have adjustable explosion power.

I have a simple answer to number 3: rocket explosions scaled up are the same and dont set things on fire, thus they are incredibly awful to make a nuclear warhead out of, and clipping grabbers and bombs together just makes things explode on load (LOL that rhymed) and doesnt work AT ALL.

use multiverse to upscale a bomb as a prop in the level, then build your machine around it to use that bomb as a nuke. [it's gonna be the size of a moon before you can have a working nuke though]