Here are couple of things i would like to see happen:
1.) -Ash winning Kalos league bringing back some of his older pokemon which weren't used for long time(like Kingler and Muk), and challenging E4 after wards.
2.) -Ash meeting his father before anime ends who happens to be pokemon master, having final battle against him to show if he is ready for such title.
3.) -Serena going through several occupations and activities. Like trying herself in Battle Maison, entering races (expanson from Rhyhorn racing), trying to become pokevision idol or pokemon explorer wanting to dedicate herself in discovering new ways of pokemon going through mega evolution.
Since various items exist to trigger this power like mega reing, mega earing, mega bracelet etc. And in some cases pokemon dont need item to mega evolve awakening its primordial strength naturally.
4.) -Clemont knowing passion he has for science and gadgets being involved in some sort of competition for inventors.
Diving more into his own thoughts and from where interest in science and mechanics originated in first place, working on improving his creations to prevent malfunctions and developing higher selfesteem thanks to that.
5.) -have writers come up with big showdown between Giovanni with TR organization against Team Flare leaded by Lysandre. With both teams pursuing after most powerful mega evolved pokemon to use them for their own purposes.
Kalos king(AZ) from games and his pretty dark background revolved around ultimate weapon and havoc this caused in past sounds like really interesting storyline. If handled right it could bring whole unexpected twist and something entirely different and innovative as far as villain storyline goes.
6.) -May coming back for 7 to 10 episode arc promoting Omega Ruby and Alpha Sapphire remakes, returning contests for abit. Returning some of her rivals like Harley or Drew following her in same region she is traveling through enjoying in their outburts, silly spats and peculiar characterization(i especially miss Harley).
7.) -Max receiving his first pokemon and starting journey, having promised battle against Ash before end of series. I could see him with bunch of powerful Psychic pokemon showing he knows how to approach them judging by Jirachi, Ralts or Deoxys bonding he achieved.
8.) -Paul appearing at some point revealing how rematch with Brandon went, coming of as winner.
9.) -in case Kalos has filler arc like BF or Orange islands were i would like to see Ash, Serena and rest of gang bumping in Misty at some point joining them for half or whole season.
Leaving gym with purpose of advancing water master dream after learning everything she could there by expanding on what Whirl Cup and sea priest Maya established in creating new water competitions through which progress would be measured (for example underwater battles seem like cool idea).
Maybe entering tournaments, races, tests organized by E4 Siebold from Kalos to test out water trainers and see if there is someone worthy enough to become his apprentice with Misty seeing this as chance to make name for herself and learn from very best about secrets of how to become type master.
Maybe promote mega evolution of Gyarados as well while catching new rare pokemon. She did dreamed of visiting France and her flirty, curious and strongwilled character could mesh great with Serena, Bonnie and Clemont imo but Ash too after so much time .
Many of this things are just wishful thinking, but still i would be glad if they happened.
