From every generation, there's been one starter who's final evolution is noticeably faster while the other 2 have mediocre-bad speed. They were:
Gen I: Charizard Gen II: Typhlosion (had the exact same base stats as Charizard) Gen III: Sceptile Gen IV: Infernape Gen V: Serperior
Froakie would be interesting since there hasn't been a fast water starter yet but I think Fennekin would be more likely. I'm not saying that they'll follow this up again for certain but it seems like they would at this point.