I'd like a rival similar to N and Colress in Gen 5, they have a mysterious personality and you learn more about them as you progress through the game. Just make the battles more frequent and have the whole shocking twist thing come up later in the game, and make it, like, dramatic. I think Colress' reveal wasn't until near the end, right? I can't remember because I already knew he was a Plasma before even playing the game. The way Unova handled rivals, I think they have character development nailed, I just want to see a change in how the rival knows you.