In general, I'm liking the addition of shock damage.
However, three things are worth pointing out.
1. It's going to make accepting a higher chance for an engine or reactor to explode even harder to justify. Boosting these components, because it also costs additional fuel, Gallicite, and ship build cost, ought to be a legitimate design tool. However, it's not hard to set up a chain-reaction, where the loss of a single 1 HS component may trigger the loss of the ship due to explosions causing explosions causing ...
There's a simple fix that keeps the exploding penalty serious, but prevents it from getting out of control. If damage occasioned by the explosion of any internal component were to not cause additional explosions, this would restore both balance and variety to this aspect of ship design.
2. Component Hit To Kill (HTK) per Hull Size (HS) varies greatly with component type. This is fine. What is already causing balance issues and will now cause bigger ones is that HTK/HS varies with the size of a component. Consider fuel storage, sensors, engines, and empty armored 1 HS missile magazines as examples.
I don't want to game ship design to improve ship durability. Let's even out HTK/HS as a function of component size, please. Let's also introduce fractional HTK. 0.5 HTK would mean that the component has a 50% chance of reducing remaining damage by one on destruction; 1.5 HTK would mean that the component reduces remaining damage by one, plus a 50% chance of another, on destruction.
3. Railguns are already somewhat inferior to lasers in beam combat (this statement does depend on how much we value the superior armor penetration power of lasers). They're currently a solid overall choice because of their superior ability to stop missiles targeting other ships, but a relative combat nerf to railguns would nevertheless be unhelpful.