I'm unsure. When Ravenclaw was in the lead by like 1,000 members or something like that, Slytherin was in second. For the most part, Slytherin is the one that's always had the least amount of members. Even thought they're closer now, I don't think all too much that the amount of members in the houses would play much of a threat against ones with lesser numbers. If you think about it, the way the house functions probably will play more of a threat. To my knowledge, since Pottermore opened, most of the time it was Ravenclaw and Slytherin neck and neck for the lead and that makes sense when you look at the house with both of them being achievement-oriented houses. At the moment, Hufflepuff is in last place, and it's the house with the second largest number of members. Slytherin is the one with the least, and it's only 400 points away from getting the lead again.