Could we get decoys for missiles, that would generate heat/EM to confuse enemy sensors? Would this be too hard to code? Event if in flight missiles do not ever retarget, it would be nice to be able to confuse new missiles and generally enemy groups.
How would this be different from missiles with no warheads? Or do you mean missiles that put out enough EM or Thermal radiation to appear to be ships? (In which case, there would need to be a way to specify exactly the output desired, or one risks having to choose between signature 268 and signature 262 decoys, when one fields signature 264 ships. )
If C# is anything like VB aurora in terms of ship identification, it would be able to tell if two 264 signature ships were the same class or not, even if one was an identical copy of the other's design and tell individual ships of the same class apart. Which, ok, not unrealistic, even ships of the same class can be expected to not be identical and have their own tells; they're not just a bright point of genetic IR light against the black(heck, you can get a ton of data from a pinpoint of light to fingerprint what's causing it).
KISS approach might instead to be able to select what design(if any) you want your decoy to fake, and maybe what specific ship of that design(if any) you want to fake(maybe allow some range of similar designs, like those that can be built at a shipyard without retooling to reuse a mechanic) when you launch them. Maybe add a "launch decoy and cut engines" order or something so the other side doesn't briefly see two of the same ship on thermals before one goes cold and gives the game away. I expect that would be the simplest to program, mostly just making the AI smart enough to handle it, tho that would be no small task in itself.
Actually I think actual KISS for just handling self-defence missile decoys and not tricking the NPR/etcs and the ilk would be to just have a decoy missile component that needs X MSP of Decoy per HS of ship - maybe a tech line for it - with a line in the missile description like "can protect ships up to X tons", size instead of thermal or EM for simplicity and most missile attacks use active sensor locks via ship fire control links anyway(and needs to be atleast fast enough to keep up) so you can't stick a thousand in your magazines and they need a large launcher with a naturally longer reload, while also needing to have ECM. Fat decoy missiles + fire control(maybe a fixed size Decoy Controller instead), launched decoys travel in the same location with the launching ship until out of fuel or destroyed or the FCS is lost, maybe one decoy per FCS or something to limit the ability to spam them; incoming missile salvo has a base chance to attack a ship's decoys instead of the ship based on ECM/ECCM calcs, say 30-50% at equal tech(better if you're more advanced, worse if you're less), and attack the decoys like they were AMMs but maybe with increased miss chance than normal because it's a dedicated platform(using missile agility to improve decoy suitability is a thought but I think that's going agay in C#? Might have just been chatter, can't find Steve saying it was being removed at the moment but I may've missed it), missiles left to attack if all decoys are destroyed resolve their attack against the target ship as normal. Need to add some new components and add a decoy component to missiles, decoys are just missiles that follow the launching ship, I think the only real system that would need any changes would be the missile attack resolution to slot a decoy phase in; it's probably not quite that simple shouldn't be
too bad. Assuming it was felt to add enough to gameplay, anyway; making missile decoys meaningfully distinct from ECM and AMMs. . . well the game already has a lot of ways to defend against missiles. I was thinking something almost like a towed torpedo decoy here, thematically/mechanically.
Tho I suppose it could simplify a bit if focused on that concept with a spinal-like one-per-ship Towed Decoy Launcher(or something) checkbox in missile launcher design, neatly solving the issue of balancing just-add-more-decoys issue; attack check sees if the towed decoy launcher is ready and loaded with an adequate decoy for the ship size, if so it resolves the attack against the decoy, if the decoy is destroyed the decoy launcher reloads, no need to launch anything under the assumption that decoys not destroyed are simply recovered.
But at this point we're pretty far from the whole deception and trickery angle.