Since Ash now rotates Pokemon in his team, I don't see a reason for him to get another Pokemon. I do, however, have speculations for his Pokemon team at the end of the saga, as well as Iris' and Cilan's:
-Pikachu
-Unfezant
-Oshawott
-Emboar
-Servine
-Scrafty
-Leavanny
The reason why I left Oshawott unevolved is because it's just too cute to evolve, plus none of Ash's Water Pokemon evolved since Kingler in the Indigo League.
Iris:
-Haxorus (in the journey's very end)
-Excadrill
-Emolga
-Deino
-Vanilluxe
-Mienfoo
I figured I'd give Iris another Dragon Pokemon to travel with, as well as a couple more cute Pokemon.
Cilan:
-Pansage
-Crustle
-Pawniard
I don't think Cilan will be getting a lot of focus when it comes to Pokemon, but I also don't know if Pawniard suits him.
And as for Team Rocket:
Jessie:
-Swoobat
-Heatmor or Durant
The reason why I said Heatmor or Durant is because in Hoenn-Sinnoh, Jessie owned one half of Hoenn's rivalry duo, Seviper.
James:
-Yamask
-Ferroseed and/or Maractus
I think that James would treat Yamask in the same way he treated Chimecho and Mime Jr. I also gave him Ferroseed and/or Maractus because of the recurring gag that James has a Grass Pokemon that shows affection while unintentionally hurting him in the process.