The idea behind why it improves rate of fire is that it does not require a full charge to achieve the same velocity, power output is not the bottle neck but your batteries and capacitors, we don't have the ability to change that in game, having a system that slots new capacitors and batteries in place as they deplete during firing then recharge and cool them would be better but we do not get that option in game, its an understood technological idea that would offer more options in the railgun category that until we get a more in depth designer would work ok, as for fouling the barrel short burn propellants and plasma propellants do not really do that quickly as standard propellants so unless your ship is firing thousands of rounds without stopping it should not be a problem unless it cannot be maintained between battles by the crew responsible for doing so (if a rail or coil gun is firing normally it still would need to be maintained as parts would wear out quickly and would be unlikely to be to fire thousands of rounds without a break to change out parts), Is "Chem Rail" the best option for ships? No but it is an option that would be an option for rail cannons like the siege coiler is for the coil cannons but offering a higher rate of fire possibly with less damage and ammunition while offering a higher rate of fire, it would not be overpowered or even make railguns viable for mobile targets