I think that just the Kanto starters will get new abilities. Not all previous starters, Even though HGSS allowed people to get one starter from each generation (except Gen 4).Blastoise: Shall Armor
Charizard: Intimidate
Venesaur: Natrual Cure
Fraligator: Water Veil
Typholsian: Flash Fire
chickoreta: Flower Gift
Mudkip: Earthquake Spiral
Fire chicken: Quick Feet
Sceptile: Herbivore
Empoleon: Thick Fat
Torterra: Earthquake Spiral
Infernape: Guts