I agree on all points except leveling to 100. People will definitely be doing that, because of Hyper Training, so if the Gen 5 scaling is back, then that will be a pain.
Still, aside from that, please bring the Gen 5 scaling back! I absolutely loved that in BW/B2W2.
I think Hyper Training is going to be something very useful, but niche. We still need to know how expensive bottlecaps are, if nothing else
Anyway that said, there will probably be SOME trainers with high levels so the diminishing returns will probably not be too much of an issue.
If the Gen V Exp. system is back, I'd assume that they'd add high leveled trainers to grind off of so that the diminishing returns aren't that much of an issue (if at all). B2W2 and Gen 6 as a whole was pretty kind in that regard and I don't think GF wouldn't accommodate for it to at least some extent.
XY was kind of, ahhh, rough. The Restaurants weren't the best way to grind. They were basically puzzle battles and very tedious to get through. The upper most level one also has a nearly guaranteed money loss unless you use literally every single possible money doubler in the game and play each match perfectly. The Battle Chateau was also just...not great. Infinite trainers, but a weird money sink and it took a while to get going and it was just so bland and most trainers didnt have a lot of pokemon. In retrospect I think the Chataeu wanted to be an equivalent to Black Tower/White Treehollow but it just didn't hit as well due to trainer team composition and trainer locations.
The e4 also took an eon to get through if for no other reason than the long room introductions.
ORAS was better though. You had secret bases, rematches and the e4 only ever played their room intros once. The worst parts were just how secret bases were once a day dealies and rematches were compeltely random.
Someone at gamexplain mentioned that they went back through a route in their 2 hours, and some of the trainers seemed to have refreshed themselves. I'm very curious if that was a legit thing or if he just forgot to fight some trainers; no one else really mentioned it outside the impressions video. Course all this would be solved if they just BROUGHT BACK THE VS SEEKER