Lydario would be making millions (before he went rogue and stared becoming an artist).
As for adding something, I would add a tool that at one point allows you to use your gear/tool for HM use, rather than depending on Pokemon to do so. I know that this has always been a canonical feature of Pokemon, but enough! I can only tolerate Kingler, Tropius, Gyarados, and Bibarel slave move-set iterations for so many years!
Also, not really add, but bring back diving, spelunking underground, and secret bases. All were very fun and added more depth to the Pokemon over world. Diving really needs to come back. And not this new diving where you go to a place with no wild encounters. I want Chincous and Relicanths, and Kinglers, Octilleries- I want them all! The music was awesome, finding treasure was fun, it was a real nice part of Hoenn that I know a lot of people still miss. And it's not like there isn't room for it. Surf-able areas in Unova were pretty slim. And with all that scenic crap in Castelia and the bridges, we could have had some nice areas underwater to battle and raise Pokemon in.