I dislike how rare radiators are in science fiction, considering how important they are in space (at least with our current tech, anyways), and how cool they are. For this game, they would also add a whole additional layer to building space-craft. I would love if things like thrusters would generate a lot of heat which would need to be dissipated by connecting radiators to them and some sort of coolant piping system when out of the atmosphere. I would suggest that builds slowly lose some heat automatically, whether that be just an estimate from the mass of the build, or something more complex like calculating the exterior surface area of the craft and the materials used... however in most cases when using thrusters that wouldn't be enough, and some sort of radiator block would be required.
This suggestion would also meld into survival very nicely, as your spacecraft might heat up beyond tolerable levels if the heat is not dissipated.
For non-survival modes, I would suggest that components either start shutting down or losing efficiency past a certain temperature, or even take damage once damage is implemented into the game.
I understand that features like this involve a lot of work to implement, pushing back optimizations, bug fixes, and other new features, so I don't really expect this to be implemented... but I saw that nobody had suggested this yet, so I thought I should put this out there, just in case. :)