Paul was undoubtedly the best rival the show has seen thus far. I think he was too big and important of a character for them to fase out completely. I'm quite sure he'll get a cameo, or at the very least, a reference in BW.
May,Misty,Dawn Brock etc are much more popular characters than Paul was and as you can see they didnt returned.Someone who has smaller fanbase and less of importance will have even lower chance to return.
Now its not impossible for Paul to show up(afterall Gary did),but i wouldnt get my hopes up if i were you.
I You'd be a fool to think that Gary was a better rival than Paul, he was virtually better than Gary in every aspect.
People have different opinions and just because you may find Paul being better doesnt mean how others will share the same view as you do.
Both Gary ad Paul were good characters having their up and downs,and it depends on someones personal preference which one he would view as "better".
You all need to understand that even though some characters are great, that doesn't mean that the writers are going to keep them on the show forever and not make room for new ones. This goes the same for everyone else. Everyone needs a chance.
And yet writers dont give every character from games a chance,with several important ones like every playable male protagonist from games being ignored with Brock being choosed over them,girls like Marina or Leaf being ignored etc.
Which is a good thing because if they were to include every one of them place would become too crowded.
Prime example of this is constant girl replacing causing consequence of older ones being neglected,instead of focusing on characters they already have giving them more of chance to be developed being left forgotten.