So what happens if your opponent also happens to be running DSC? It's not exactly an uncommon card in Vintage.
It's becoming less common. However, this is the biggest problem I've faced so far; I'm not sure whether Leyline of the Void would be a way around this due to replacement effects (ie whether Leyline or DSC goes on the stack first), I was thinking maybe put some Extracts in my sideboard?
You lose to Fish, Combo, and Ichorid, and anything that runs DSC. That's ... a lot of problems. The problem with this deck is with the underlying strategy, and it isn't going to be shored up by adding or changing one or two cards. Sometimes we have to accept that certain ideas just won't work or are not appropriate for the current metagame.