That's an interesting build, I had given up on railguns after they added the annoying lag-delay to them but plasma slug mod would really change them quite a bit as you could take more shots without worrying about the limited ammo. I'm tempted to give this build a try although at the moment my Python's class 2 hardpoints are fitted for beam turrets as this helps me keep consistent fire on smaller fighters. Swapping them out for class 2 railguns would definitely improve my damage against larger ships, assuming I can be bothered to farm all the mats to try for the plasma slug mods. I might wait until 2.1.2 drops to use favors to get the right mods because at this point I am tired of farming for grade 1 mods and rolling literally 100 times to get a mod I want.
As a side point, I think I've seen some of your videos before, didn't you post one where you put 5 plasma accelerators onto a dropship and obliterated clippers at some point? That was pretty hilarious, I've been a huge fan of plasma weapons due to the high alpha damage when used accurately although I've stopped using them since 1.6/2.1 launched because the NPCs move too fast to reliably target their subsystems. Rails have a high enough shot speed that they might make a sniper build viable again if they aren't ammo dependent.
My only real issue with some of these builds is that the drop rate for some of the very rare mats makes it take too long to get a grade 5 with the effect you want, mostly because of the limited amounts of modified embedded firmware. Even WITH favors to select the specific mod you're looking at a LOT of firmware to get the rolls so it's not really viable at the moment. Hopefully this will change with 2.1.2 depending on how they handle favors and if they change the drop rate for some of the very rare firmware mats.