"somewhat informed" I like that.
There are so many things from the unpublished Silmarillion that crept into the published Hobbit and LotR that one cannot help but think that Tolkien had despaired of TS ever being published and didn't want all that hard work and creativity to go to waste. The Arkenstone would look to be one. If it were an actual silmaril, though, I would wonder how Smaug, a creature of evil, would manage to keep it around without being either burned or driven mad by it.