It shouldn't really matter. It's the same thing as having a huge debate about why the new Stormtrooper weapon has White on it -- it's the same ball park. All that should matter that it does what it's supposed to do. The Saber can cut off some limbs and the gun can shoot some rebels so there should be no real issue with the weapons at all. Then again I am open to change, other people may be more skeptical about it, which started with Episode 1 and the Staff Saber. There will always be large discussions about it until the movie releases and we actually see for ourselves the practical side of introducing a new weapon, just like with Episode 1. The movies speak for themselves. From what i've seen from the trailers it looks like it can do some damage so that's all I really care about. But to bring up what you said about an ancient Sith weapon.. you may actually be onto something there. Since when the concept art for TFA was leaked there were discussions of Kylo collecting "Ancient Artefacts" including Darth Vader's helmet. So it may well be what you say.