Well as I stated a bit earlier in the thread, this is definitely not a cider anymore, with an alcohol percentage of around 13 by volume, this is definitely a fruit wine. Having said that, using blueberry juice instead of a mixture will certainly up the blueberry flavor a ton, since I used very little blueberry juice relative to apple juice. Also, that would be insanely expensive, since blueberry juice is considered one of those top shelf juices. When I bought the juice for the secondary additions, I believe it would have ended up being in the neighborhood of $30 a gallon, compared to $2-$5 for apple juice. So for a 6 gallon batch, that would be $180 for the juice alone, plus fruit if you chose to use it. Having said that, if you are able to buy blueberry juice much cheaper, then go for it, I imagine that would make a fantastic blueberry wine.