I'm not commenting in too deep until we have any confirmations.
- No Gym Leaders: that's surely revolutionary and odd for a main Pokémon game, but I must admit that recently the Gyms felt really useless. I loved XY charachter designs, but I can barely remember the Gyms: too easy, really nothing to prove "your strenght" as they were supposed to be. I was surely hoping for a change, this sound a bit drastic but if rightly executed is still better than same forgettable Gyms as in the latest games.
- League build around you: if absence of Gym Leaders sounds odd, this is even weirder... I'm not negative about it at all, I'm just really confused on how to manage this thing making it more entertaining than the League itself. However, the presence of "Island Leaders" and later e4 seems to indicate some kind of solid replacing.
- Riding Pokémons: I doubt we'll be able to actually ride almost any pokémon... Maybe a lot more than in XY, and that's cool, but there're tons of minuscule and gracile mons incapable of supporting a person for a ride, at least graphically. However, if this is real, I'm really hoping it'll be the same for surf and fly (fly should become as Soaring in ORAS for any pokémon big enough to be animated like that). Even the pokémon popping out for moves like Strenght, Cut or Rock Smash would be cool; especially for Strenght, I always found pretty ugly seeing the trainer itself moving the rocks.
- New Bracelets: If real, hoping that this new kind of evo will be differentiated enough from Mega evo, and not mutual exclusive. I wouldn't like to miss potentially great Megas 'cause of this new mechanics. I'm not too fond of Ash-Greninja (mostly 'cause of the hair reference), I'm really hoping it'll be an exception design-wise reserved for the anime, so the "normal synchro evo" wouldn't be identical to the Ash's one.
-New mons: New Mushroom is ok, I really didn't feel it necessary since it's quite full of mushrooms in Pokémon (Amoongus, Breelom, and partially Parasect and their respective evo lines) but if unique enough no problem; rugby monkey not really my thing but could be cool; dolphin... FINALLY (but when a dolphin 'mon is up in the air the risk of a fake is really high); Snowman, I guess Abomasnow was too owl/conifer-like? I'm ok with that, not terribly excited though; Sea Cucumber has the potential to be the "dumb pokémon" of this gen, it would be nice to see a something useful, maybe bulky with a decent defensive ability.
-New Overlord Pokémon in each District: not really sure what this means, but ok... Are these the fellow guardians of Tapu Koko?
- Starters: If this is real, those infamous leaked sketches are actually true... And I'm pretty happy about them. That final Rowlett is probably one of my favorite starter ever, I love it, it's unique, complex but not overdesigned, and has the potential for some cool arrow-related signature moves or pseudo-signature (hidden) ability. Despite all the hate, I love the final Pupplio too: I think it's really beautiful and the concept of a Selkie/Mermaid make it unique compared to the other pinniped 'mons. Water/Fairy would fit it perfectly and it's a great typing. Finally the obviously most controversial of the three: wrestler final Litten. Ok, I would be disappointed by it, not 'cause of potential fire/fighting, but 'cause I really don't like the habit of transforming animals in humanoid pokémons, I would have preferred something more inspired by actual felids or other quadruped carnivores. However, that said, for that concept I think it's freaking cool, luckily it wouldn't be the Chesnaught of this gen. Actually, if that design is confirmed, I don't really care if it'll be the logical fire/fighting or fire/dark or fire/ground, I'm more conflicted about the concept of "fire starter fighter" than its typing alone. Emboar was a much better candidate for Fire/Ground.
- Werewolf Rockruff Evo: That would be in line with Rockruff description, and we don't have any werewolves yet, so I find it cool. Rock/Dark isn't common either, and if it'll be fast it'll be pretty original and could have some potential.