Brock should appear at Kalo league as a Doctor !

[Famon]

Yep , I believe Brock can reappear in Kalo League as a Doctor helping out Nurse Joys !
After all , We already know busy Pokemon center are during League conference at Indigo League.
So Brock can appear as a extra help .
He can also--

-- Flirt with Nurse Joy , Aria and Alexa .

-- Get Advise from Bonnie about Wooing Girls.

--Give Clemont some helpful tip about handling little sister (Since he has so many)

Off course , Misty can reappear with Ash's mom and Prof Oak at Kalo league . Specially If Ash reach the final.
Then may be , we can have a filler episode focusing on Original Trio (Ash , Brock , Misty) growth and friendship One day before the League final.
Just imagine Ash , Brock and Misty talking about how they met and grown with a lot of Flashback.
However , It would have been possible if Kalo was Ash's final League that he wins.

 

[Bobbylicious]

Brock is racist bring back Tracey!!

But ash should release goodra and then iris can catch it and beat him with it in the kalos league :)

 

[DarkWitch]

That would be pretty cool seeing Brock again.
If I could see both Brock and Misty again I would be so happy.

 

[weedle_mchairybug]

As long as Brock tones it down regarding his more Glenn Quagmire-esque behavior, I won't have any problem with him returning.