So, let's see what we know:
+ TR will capture a Stufful, apparently. I guess this will to compensate the evidence that Bewear will no longer be with Team Rocket once the Alola's adventures are over.
+ Misty and Brock return and visit Ash on Alola. I don't know why, but I hope it will last for the whole season. I really miss these two.
+ We finally see Hau, and apparently, he has a Dartrix. I guess this confirms there will be a Alola League and Hau will be part of it.
+ It surprises me the fact of Ash capturing an Eevee, but I guess it's to promote "Let's Go Pikachu" and "Let's Go Eevee". I think it will be fun.
Now, things I hope to see:
+ We can't see Ash's other Pokemon in the poster, so I hope for the best: Torracat evolving to Incineroar, Rowlet evolving to Dartrix (and later, to Decidueye), and possibly, another surprise.
+ More UltraGuardian missions: Ash't team still hasn't face Pheromosa, Kartana and Guzzlord. This last one will surely bring a great plot. Probably envolving Team Rainbow Rocket.
+ Ash's last trial: Ash still has to go to Poni Island and and face the last Grand Trial. For the Ground Pokemon, he better makes Rowlet evolve. And if he has to fight the Dragon Pokemon, I don't see how he will do it without Poipole. I guess his best hope is for Torracat to evolve to Incineroar and learn Outrage or Dual Chop (better this one), and since they are half Fighting types, Rowlet/Dartrix/Decidueye evolving and learning a powerful Flying move. While they are at Poni Island, surely Sophocles Charjabug will evolve to Vikavolt.
+ Team Skull: We still haven't see these guys properly, outside of its "Three Stooges". Guzma and Plumeria still have to debut.
+ Alola's League: This will be surely the last episodes of the season, right before the start of the new Generation and Ash going back to Kanto. Since this would be the very first edition of the Pokemon League in Alola, there's a chance for Ash to win it.
+ Team Rainbow Rocket: Even with Necorzma's arc ended, Team Rocket could still be after the other Ultra Beasts to create an army, so there's still the chance to see Giovanni and the others here as the big villains. Not to mention the chance to see the past villains from other regions too.
+ Nature's Madness: In order to defeat Team Rainbow Rocket, I believe the Alolan Guardians will need the help of the UltraGuardians, and they will possibly share with them the power of their Tapunium Z to make their Z-Moves against Team Rainbow Rocket.
+ Marshadow: This Legendary Pokemon should appear officially; after all, it already made a cameo back in the episode where RotomDex lost its body.
+ Mew and Mewtwo: This will probably happen in the next movie, but because of Team Rainbow Rocket, we could see the return of both Mewtwos here. They could finally debut both Mega-Evolutions in the Anime. And Mew could appear with its Z-Move, Genesis Supernova.
+ Ultra Recon Squad: Team Rainbow Rocket's plot could bring us the debut of these characters. They will surely amplify the intensity of the plot.
+ Poipole's Return: Team Rainbow Rocket will definitely appear, and if they manage to cross an Ultra-Hole or something, this could give us the return of Ash's Poipole. And hopefully, this time, he will stay with Ash and it will evolve.
+ Mantine Surf: If Hau is going to debut, it's very possible that this mini-game will debut too. And it does, Ash's Pikachu could finally learn to use the move Surf, which will be a great asset for our favourite Pokemon.
+ Ash's Greninja returns: Before the Pokemon League starts, I wish for the return of Ash's Greninja for this Pokemon League. If the Pokemon School makes another trip to another region (hoping for Kalos), it would be a perfect chance to bring back Ash's Greninja, just like Ash's Charizard returned previously.
Well, what do you think?