I see it more of a classic "
build up the new guy by have him defeat the guy who previously defeated the protagonist". Ash lost to Alain, and now Alain is going to lose to Leon, a shortcut for viewers since the Kalos League that Leon is on a whole other level that Ash previously couldn't even beat the level before it. Ash has grown since then of course, and without a battle against Alain we don't know if Ash can beat him now, but at the moment that doesn't matter to set the mood.
Also, considering Ash is facing Steven and he just trained against Paul's Gyarados, Garchomp, and Metagross, I feel it's kind of weird it's not Cynthia vs Lance next to Ash vs Steven (with Iris vs Diantha next to Leon vs Alain). And aside from Iris vs Cynthia where there's a little connection there, these battles don't really seem that exciting.
... You know what, I'm gonna say it: Ash loses to Steven. I think they're going to pull a major twist of just having Ash lose round 1. We're going to be shown that, not only is Ash not on Leon's level, he's not on ANY Champion's level (aside from Iris... and we don't know whether she became Champion because she beat Alder (who, let's be honest, isn't supposed to be a strong Champion) or because Alder already gave up the position so she just had to beat other potential candidates which isn't quite the same as beating the Champion). Iris and Alain also loses against their opponent pretty handily, with the only Round 1 match being close is the one against the experienced Champions: Leon & Diantha.
So going to say Round 2 would be Leon VS Diantha and Cynthia VS Steven and final round being Leon VS Cynthia with Leon winning.
RIP, prayers from his family & friends, he may not have been here long, but he certainly left his mark.