Now there is a lot of things to consider here. You must realize that someone will need to find the fastest way of flushing the entire roll down the toilet. However, the toilet will flush in different directions in different parts of the world and the different models of the toilet. What one doesn't realize is that the toilet paper itself is a parameter that would cause tremendous problems being placed different ways, like those thick ultra powerful bear tissues or those 4 rolls in one. That means that some toilet paper will have a tight fit in the socket. Lots of lube will be needed to move such roll, and depending on the direction of the lube applied the paper will go that direction.
In conclusion, the direction of the roll will depend on the luube applied.