Your post was ridiculous since it's been possible to just put a railgun on a ship for the longest time and in all practicality it is "spinal" railgun. No offense intended but I just had to ask.
It's very weird to be singling out Arwyn, when he wasn't the first one to talk about spinal railguns and Steve himself said he was looking for ways to implement them in this thread.
However, you bring up a good point that the current implementation of spinal weapons doesn't really make them unique enough.
Currently spinal weapons are basically just slightly larger variations of normal weapons with the unique limitation that you can only put one of them on a ship.
That means the current spinal weapons are fixed size. I think it would be much more thematic for a spinal weapon to be a custom size depending on the size of the ship they are built into, in contrast to normal fixed size weapons. So you would just research a generic spinal mount version of a particular laser, for example, and then its stats would only be determined once you actually put it on a ship, cause the stats would be modified by the total size of the ship. That would mean a spinal weapon would be custom built for each class that they are used on, which makes more sense to me than them being the same size no matter what ship you put them on.