The whole stone thing is likely something you find out within the first hour of the game. As for the game, I honestly don't know what to think. I knew it was going to be like the 3D models, but if they keep GTI's gameplay design, I'll have to pass. I mean it was like they were trying to make an overly tedious system even more tedious to the point I never want to touch it again. The story is worth watching imo, but it's not worth the horrible design.
Now let's look at the new one. We already know all the Pokemon will be included, but the cinematics really make me worried. In all the previous titles, only a handful of 5 legendaries took a big part of the story while the others were simply bonus bosses. With this big emphasis on Legendaries, I think it's going to kill the plot. There is such a thing as too many characters and a combination of townsfolk combined with what seems to be at least 15 legendaries involved (and likely 5 that won't be revealed) characters are going to become even more shallow (or a plot that is twice as long as EoS). I'm just basing this on previous games in the series and I don't see this working...well.
I'm a big mystery dungeon fan and played all of them (and yes, I like GTI even though it's disappointing). I just have mixed feeling about this game. EoS really help correct some faults in the Explorers series so I hope this game does the same for GTI. I can pretty much guarantee you and the partner bonding will be well done, but I cannot say for the rest of the story. It'll likely be worth buying though...I just hope they don't screw up with this whole legendary concept.