Nacreous
Fire trainer
Well,Empoleon ended up Water/Steel so,I don't think that's an issue.Apart from Samurott and Serperior, all starters learn Earthquake. If its Water/Flying it probably won't be an issue.
Unfortunately, it probably won't be Water/Flying as that removes Chespin's advantage over it unless it becomes Grass/Rock or Grass/Electric. The former is more likely, but that means Fennekin would have to end up part Bug, Steel, Ice or Fighting to keep its advantage and all those types seem unlikely imo.