Maybe the whole line of reasoning is flawed. Err, that Gamefreak likes to hide secrets and surprises that is. Looking back at "remakes," I seem to remember gamefreak being very open with the new stuff in a remake or 3rd edition game, especially with new forms.
Platinum had the new Giratina and rotoms shown before release, B2W2 had the genie trio and Kyruem forms well known before coming out, I believe the Sevii's were teased before FR/LG came out, Emerald was all about the Battle Frontier, and HGSS was all about... walking with your pokemon? I can't remember.
And, they kind of have to be. Since they are essentially trying to sell you on a game that's already come out before. For most people, graphical updates just aren't enough to cut it, so Gamefreak decided to lead with the main course rather than the appetizer. Or to remove food anaolgies, they showed off the megas in case "RSE remake" wasn't enough to satisfy.
I guess my point is that revealing everything before it comes out isn't a new practice, especially when it comes to remakes. They aren't selling you on exploring a new world, they are trying to get you to re-explore and old one. So while there may or may not be any more hidden legendaries or megas or tutors, don't act so shocked at this BOLD NEW BETRAYAL. Because it isn't. And it's not even a betrayal, just advertising.