I think it is too early for us to talk about popularity. We should wait until GF plays their ace card. Popularity of a Pokemon is defined by GF not the fans. We don't have any say in this, they know how to make people like some Pokemon and obviously they will do it again.
As far as popularity based on species go, Froakie and Fennekin are already golden. Japanese kids love frogs and foxes. Every frog based Pokemon(evolution family) made it to the main cast so far. Now the starter is a frog which makes it even more likely to end up as a mascot.